Algebra Examples

$f (x) = \frac{24}{1 + 3 e^{- 1.3 x}}$

Step 1

Find the second derivative.

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Step 1.1

Find the first derivative.

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Step 1.1.1

Differentiate using the Constant Multiple Rule.

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Step 1.1.1.1

Since $24$ is constant with respect to $x$ , the derivative of $\frac{24}{1 + 3 e^{- 1.3 x}}$ with respect to $x$ is $24 \frac{d}{d x} [\frac{1}{1 + 3 e^{- 1.3 x}}]$ .

$f' (x) = 24 \frac{d}{d x} (\frac{1}{1 + 3 e^{- 1.3 x}})$

Step 1.1.1.2

Rewrite $\frac{1}{1 + 3 e^{- 1.3 x}}$ as ${(1 + 3 e^{- 1.3 x})}^{- 1}$ .

$f' (x) = 24 \frac{d}{d x} ({(1 + 3 e^{- 1.3 x})}^{- 1})$

Step 1.1.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{- 1}$ and $g (x) = 1 + 3 e^{- 1.3 x}$ .

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Step 1.1.2.1

To apply the Chain Rule, set $u_{1}$ as $1 + 3 e^{- 1.3 x}$ .

$f' (x) = 24 (\frac{d}{d u (1)} ({u_{1}}^{- 1}) \frac{d}{d x} (1 + 3 e^{- 1.3 x}))$

Step 1.1.2.2

Differentiate using the Power Rule which states that $\frac{d}{d u_{1}} [{u_{1}}^{n}]$ is $n {u_{1}}^{n - 1}$ where $n = - 1$ .

$f' (x) = 24 (- {u_{1}}^{- 2} \frac{d}{d x} (1 + 3 e^{- 1.3 x}))$

Step 1.1.2.3

Replace all occurrences of $u_{1}$ with $1 + 3 e^{- 1.3 x}$ .

$f' (x) = 24 (- {(1 + 3 e^{- 1.3 x})}^{- 2} \frac{d}{d x} (1 + 3 e^{- 1.3 x}))$

Step 1.1.3

Differentiate.

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Step 1.1.3.1

Multiply $- 1$ by $24$ .

$f' (x) = - 24 ({(1 + 3 e^{- 1.3 x})}^{- 2} \frac{d}{d x} (1 + 3 e^{- 1.3 x}))$

Step 1.1.3.2

By the Sum Rule, the derivative of $1 + 3 e^{- 1.3 x}$ with respect to $x$ is $\frac{d}{d x} [1] + \frac{d}{d x} [3 e^{- 1.3 x}]$ .

$f' (x) = - 24 {(1 + 3 e^{- 1.3 x})}^{- 2} (\frac{d}{d x} (1) + \frac{d}{d x} (3 e^{- 1.3 x}))$

Step 1.1.3.3

Since $1$ is constant with respect to $x$ , the derivative of $1$ with respect to $x$ is $0$ .

$f' (x) = - 24 {(1 + 3 e^{- 1.3 x})}^{- 2} (0 + \frac{d}{d x} (3 e^{- 1.3 x}))$

Step 1.1.3.4

Add $0$ and $\frac{d}{d x} [3 e^{- 1.3 x}]$ .

$f' (x) = - 24 {(1 + 3 e^{- 1.3 x})}^{- 2} \frac{d}{d x} (3 e^{- 1.3 x})$

Step 1.1.3.5

Since $3$ is constant with respect to $x$ , the derivative of $3 e^{- 1.3 x}$ with respect to $x$ is $3 \frac{d}{d x} [e^{- 1.3 x}]$ .

$f' (x) = - 24 {(1 + 3 e^{- 1.3 x})}^{- 2} (3 \frac{d}{d x} (e^{- 1.3 x}))$

Step 1.1.3.6

Multiply $3$ by $- 24$ .

$f' (x) = - 72 {(1 + 3 e^{- 1.3 x})}^{- 2} \frac{d}{d x} e^{- 1.3 x}$

Step 1.1.4

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - 1.3 x$ .

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Step 1.1.4.1

To apply the Chain Rule, set $u_{2}$ as $- 1.3 x$ .

$f' (x) = - 72 {(1 + 3 e^{- 1.3 x})}^{- 2} (\frac{d}{d u (2)} (e^{u_{2}}) \frac{d}{d x} (- 1.3 x))$

Step 1.1.4.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{2}} [a^{u_{2}}]$ is $a^{u_{2}} \ln (a)$ where $a$ = $e$ .

$f' (x) = - 72 {(1 + 3 e^{- 1.3 x})}^{- 2} (e^{u_{2}} \frac{d}{d x} (- 1.3 x))$

Step 1.1.4.3

Replace all occurrences of $u_{2}$ with $- 1.3 x$ .

$f' (x) = - 72 {(1 + 3 e^{- 1.3 x})}^{- 2} (e^{- 1.3 x} \frac{d}{d x} (- 1.3 x))$

Step 1.1.5

Differentiate.

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Step 1.1.5.1

Since $- 1.3$ is constant with respect to $x$ , the derivative of $- 1.3 x$ with respect to $x$ is $- 1.3 \frac{d}{d x} [x]$ .

$f' (x) = - 72 {(1 + 3 e^{- 1.3 x})}^{- 2} (e^{- 1.3 x} (- 1.3 \frac{d}{d x} x))$

Step 1.1.5.2

Multiply $- 1.3$ by $- 72$ .

$f' (x) = 93.6 {(1 + 3 e^{- 1.3 x})}^{- 2} (e^{- 1.3 x} (\frac{d}{d x} (x)))$

Step 1.1.5.3

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$f' (x) = 93.6 {(1 + 3 e^{- 1.3 x})}^{- 2} (e^{- 1.3 x} \cdot 1)$

Step 1.1.5.4

Multiply $e^{- 1.3 x}$ by $1$ .

$f' (x) = 93.6 {(1 + 3 e^{- 1.3 x})}^{- 2} e^{- 1.3 x}$

Step 1.1.6

Simplify.

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Step 1.1.6.1

Reorder the factors of $93.6 {(1 + 3 e^{- 1.3 x})}^{- 2} e^{- 1.3 x}$ .

$f' (x) = 93.6 e^{- 1.3 x} {(1 + 3 e^{- 1.3 x})}^{- 2}$

Step 1.1.6.2

Rewrite the expression using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$f' (x) = 93.6 e^{- 1.3 x} (\frac{1}{{(1 + 3 e^{- 1.3 x})}^{2}})$

Step 1.1.6.3

Multiply $93.6 e^{- 1.3 x} \frac{1}{{(1 + 3 e^{- 1.3 x})}^{2}}$ .

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Step 1.1.6.3.1

Combine $\frac{1}{{(1 + 3 e^{- 1.3 x})}^{2}}$ and $93.6$ .

$f' (x) = \frac{93.6}{{(1 + 3 e^{- 1.3 x})}^{2}} \cdot e^{- 1.3 x}$

Step 1.1.6.3.2

Combine $\frac{93.6}{{(1 + 3 e^{- 1.3 x})}^{2}}$ and $e^{- 1.3 x}$ .

$f' (x) = \frac{93.6 e^{- 1.3 x}}{{(1 + 3 e^{- 1.3 x})}^{2}}$

Step 1.2

Find the second derivative.

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Step 1.2.1

Since $93.6$ is constant with respect to $x$ , the derivative of $\frac{93.6 e^{- 1.3 x}}{{(1 + 3 e^{- 1.3 x})}^{2}}$ with respect to $x$ is $93.6 \frac{d}{d x} [\frac{e^{- 1.3 x}}{{(1 + 3 e^{- 1.3 x})}^{2}}]$ .

$f'' (x) = 93.6 \frac{d}{d x} (\frac{e^{- 1.3 x}}{{(1 + 3 e^{- 1.3 x})}^{2}})$

Step 1.2.2

Differentiate using the Quotient Rule which states that $\frac{d}{d x} [\frac{f (x)}{g (x)}]$ is $\frac{g (x) \frac{d}{d x} [f (x)] - f (x) \frac{d}{d x} [g (x)]}{{g (x)}^{2}}$ where $f (x) = e^{- 1.3 x}$ and $g (x) = {(1 + 3 e^{- 1.3 x})}^{2}$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} \frac{d}{d x} (e^{- 1.3 x}) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{({(1 + 3 e^{- 1.3 x})}^{2})}^{2}})$

Step 1.2.3

Multiply the exponents in ${({(1 + 3 e^{- 1.3 x})}^{2})}^{2}$ .

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Step 1.2.3.1

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} \frac{d}{d x} (e^{- 1.3 x}) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{2 \cdot 2}})$

Step 1.2.3.2

Multiply $2$ by $2$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} \frac{d}{d x} (e^{- 1.3 x}) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.4

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - 1.3 x$ .

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Step 1.2.4.1

To apply the Chain Rule, set $u_{1}$ as $- 1.3 x$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} (\frac{d}{d u (1)} (e^{u_{1}}) \frac{d}{d x} (- 1.3 x)) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.4.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{1}} [a^{u_{1}}]$ is $a^{u_{1}} \ln (a)$ where $a$ = $e$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} (e^{u_{1}} \frac{d}{d x} (- 1.3 x)) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.4.3

Replace all occurrences of $u_{1}$ with $- 1.3 x$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} (e^{- 1.3 x} \frac{d}{d x} (- 1.3 x)) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.5

Differentiate.

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Step 1.2.5.1

Since $- 1.3$ is constant with respect to $x$ , the derivative of $- 1.3 x$ with respect to $x$ is $- 1.3 \frac{d}{d x} [x]$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} (- 1.3 \frac{d}{d x} x) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.5.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} (- 1.3 \cdot 1) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.5.3

Simplify the expression.

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Step 1.2.5.3.1

Multiply $- 1.3$ by $1$ .

$f'' (x) = 93.6 (\frac{{(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} \cdot - 1.3 - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.5.3.2

Move $- 1.3$ to the left of ${(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x}$ .

$f'' (x) = 93.6 (\frac{- 1.3 \cdot ({(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x}) - e^{- 1.3 x} \frac{d}{d x} {(1 + 3 e^{- 1.3 x})}^{2}}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.6

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{2}$ and $g (x) = 1 + 3 e^{- 1.3 x}$ .

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Step 1.2.6.1

To apply the Chain Rule, set $u_{2}$ as $1 + 3 e^{- 1.3 x}$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - e^{- 1.3 x} (\frac{d}{d u (2)} ({u_{2}}^{2}) \frac{d}{d x} (1 + 3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.6.2

Differentiate using the Power Rule which states that $\frac{d}{d u_{2}} [{u_{2}}^{n}]$ is $n {u_{2}}^{n - 1}$ where $n = 2$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - e^{- 1.3 x} (2 u_{2} \frac{d}{d x} (1 + 3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.6.3

Replace all occurrences of $u_{2}$ with $1 + 3 e^{- 1.3 x}$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - e^{- 1.3 x} (2 (1 + 3 e^{- 1.3 x}) \frac{d}{d x} (1 + 3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.7

Differentiate.

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Step 1.2.7.1

Multiply $2$ by $- 1$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 2 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) \frac{d}{d x} (1 + 3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.7.2

By the Sum Rule, the derivative of $1 + 3 e^{- 1.3 x}$ with respect to $x$ is $\frac{d}{d x} [1] + \frac{d}{d x} [3 e^{- 1.3 x}]$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 2 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) (\frac{d}{d x} (1) + \frac{d}{d x} (3 e^{- 1.3 x})))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.7.3

Since $1$ is constant with respect to $x$ , the derivative of $1$ with respect to $x$ is $0$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 2 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) (0 + \frac{d}{d x} (3 e^{- 1.3 x})))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.7.4

Add $0$ and $\frac{d}{d x} [3 e^{- 1.3 x}]$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 2 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) \frac{d}{d x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.7.5

Since $3$ is constant with respect to $x$ , the derivative of $3 e^{- 1.3 x}$ with respect to $x$ is $3 \frac{d}{d x} [e^{- 1.3 x}]$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 2 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) (3 \frac{d}{d x} (e^{- 1.3 x})))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.7.6

Simplify the expression.

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Step 1.2.7.6.1

Move $3$ to the left of $1 + 3 e^{- 1.3 x}$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 2 e^{- 1.3 x} (3 \cdot (1 + 3 e^{- 1.3 x}) \frac{d}{d x} (e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.7.6.2

Multiply $3$ by $- 2$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 6 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) \frac{d}{d x} (e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.8

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - 1.3 x$ .

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Step 1.2.8.1

To apply the Chain Rule, set $u_{3}$ as $- 1.3 x$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 6 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) (\frac{d}{d u (3)} (e^{u_{3}}) \frac{d}{d x} (- 1.3 x)))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.8.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{3}} [a^{u_{3}}]$ is $a^{u_{3}} \ln (a)$ where $a$ = $e$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 6 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) (e^{u_{3}} \frac{d}{d x} (- 1.3 x)))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.8.3

Replace all occurrences of $u_{3}$ with $- 1.3 x$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 6 e^{- 1.3 x} ((1 + 3 e^{- 1.3 x}) (e^{- 1.3 x} \frac{d}{d x} (- 1.3 x)))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.9

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 6 e^{- 1.3 x - 1.3 x} ((1 + 3 e^{- 1.3 x}) \frac{d}{d x} (- 1.3 x))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.10

Subtract $1.3 x$ from $- 1.3 x$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 6 e^{- 2.6 x} ((1 + 3 e^{- 1.3 x}) \frac{d}{d x} (- 1.3 x))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.11

Since $- 1.3$ is constant with respect to $x$ , the derivative of $- 1.3 x$ with respect to $x$ is $- 1.3 \frac{d}{d x} [x]$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} - 6 e^{- 2.6 x} ((1 + 3 e^{- 1.3 x}) (- 1.3 \frac{d}{d x} x))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.12

Multiply $- 1.3$ by $- 6$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} + 7.8 e^{- 2.6 x} ((1 + 3 e^{- 1.3 x}) (\frac{d}{d x} (x)))}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.13

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} + 7.8 e^{- 2.6 x} ((1 + 3 e^{- 1.3 x}) \cdot 1)}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.14

Combine fractions.

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Step 1.2.14.1

Multiply $1 + 3 e^{- 1.3 x}$ by $1$ .

$f'' (x) = 93.6 (\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} + 7.8 e^{- 2.6 x} (1 + 3 e^{- 1.3 x})}{{(1 + 3 e^{- 1.3 x})}^{4}})$

Step 1.2.14.2

Combine $93.6$ and $\frac{- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} + 7.8 e^{- 2.6 x} (1 + 3 e^{- 1.3 x})}{{(1 + 3 e^{- 1.3 x})}^{4}}$ .

$f'' (x) = \frac{93.6 (- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} + 7.8 e^{- 2.6 x} (1 + 3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15

Simplify.

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Step 1.2.15.1

Apply the distributive property.

$f'' (x) = \frac{93.6 (- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x} + 7.8 e^{- 2.6 x} \cdot 1 + 7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.2

Apply the distributive property.

$f'' (x) = \frac{93.6 (- 1.3 {(1 + 3 e^{- 1.3 x})}^{2} e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3

Simplify the numerator.

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Step 1.2.15.3.1

Simplify each term.

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Step 1.2.15.3.1.1

Rewrite ${(1 + 3 e^{- 1.3 x})}^{2}$ as $(1 + 3 e^{- 1.3 x}) (1 + 3 e^{- 1.3 x})$ .

$f'' (x) = \frac{93.6 (- 1.3 ((1 + 3 e^{- 1.3 x}) (1 + 3 e^{- 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.2

Expand $(1 + 3 e^{- 1.3 x}) (1 + 3 e^{- 1.3 x})$ using the FOIL Method.

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Step 1.2.15.3.1.2.1

Apply the distributive property.

$f'' (x) = \frac{93.6 (- 1.3 (1 (1 + 3 e^{- 1.3 x}) + 3 e^{- 1.3 x} (1 + 3 e^{- 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.2.2

Apply the distributive property.

$f'' (x) = \frac{93.6 (- 1.3 (1 \cdot 1 + 1 (3 e^{- 1.3 x}) + 3 e^{- 1.3 x} (1 + 3 e^{- 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.2.3

Apply the distributive property.

$f'' (x) = \frac{93.6 (- 1.3 (1 \cdot 1 + 1 (3 e^{- 1.3 x}) + 3 e^{- 1.3 x} \cdot 1 + 3 e^{- 1.3 x} (3 e^{- 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3

Simplify and combine like terms.

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Step 1.2.15.3.1.3.1

Simplify each term.

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Step 1.2.15.3.1.3.1.1

Multiply $1$ by $1$ .

$f'' (x) = \frac{93.6 (- 1.3 (1 + 1 (3 e^{- 1.3 x}) + 3 e^{- 1.3 x} \cdot 1 + 3 e^{- 1.3 x} (3 e^{- 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3.1.2

Multiply $3 e^{- 1.3 x}$ by $1$ .

$f'' (x) = \frac{93.6 (- 1.3 (1 + 3 e^{- 1.3 x} + 3 e^{- 1.3 x} \cdot 1 + 3 e^{- 1.3 x} (3 e^{- 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3.1.3

Multiply $3$ by $1$ .

$f'' (x) = \frac{93.6 (- 1.3 (1 + 3 e^{- 1.3 x} + 3 e^{- 1.3 x} + 3 e^{- 1.3 x} (3 e^{- 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3.1.4

Rewrite using the commutative property of multiplication.

$f'' (x) = \frac{93.6 (- 1.3 (1 + 3 e^{- 1.3 x} + 3 e^{- 1.3 x} + 3 \cdot (3 e^{- 1.3 x} e^{- 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3.1.5

Multiply $e^{- 1.3 x}$ by $e^{- 1.3 x}$ by adding the exponents.

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Step 1.2.15.3.1.3.1.5.1

Move $e^{- 1.3 x}$ .

$f'' (x) = \frac{93.6 (- 1.3 (1 + 3 e^{- 1.3 x} + 3 e^{- 1.3 x} + 3 \cdot (3 (e^{- 1.3 x} e^{- 1.3 x}))) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3.1.5.2

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$f'' (x) = \frac{93.6 (- 1.3 (1 + 3 e^{- 1.3 x} + 3 e^{- 1.3 x} + 3 \cdot (3 e^{- 1.3 x - 1.3 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3.1.5.3

Subtract $1.3 x$ from $- 1.3 x$ .

$f'' (x) = \frac{93.6 (- 1.3 (1 + 3 e^{- 1.3 x} + 3 e^{- 1.3 x} + 3 \cdot (3 e^{- 2.6 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3.1.6

Multiply $3$ by $3$ .

$f'' (x) = \frac{93.6 (- 1.3 (1 + 3 e^{- 1.3 x} + 3 e^{- 1.3 x} + 9 e^{- 2.6 x}) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.3.2

Add $3 e^{- 1.3 x}$ and $3 e^{- 1.3 x}$ .

$f'' (x) = \frac{93.6 (- 1.3 (1 + 6 e^{- 1.3 x} + 9 e^{- 2.6 x}) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.4

Apply the distributive property.

$f'' (x) = \frac{93.6 ((- 1.3 \cdot 1 - 1.3 (6 e^{- 1.3 x}) - 1.3 (9 e^{- 2.6 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.5

Simplify.

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Step 1.2.15.3.1.5.1

Multiply $- 1.3$ by $1$ .

$f'' (x) = \frac{93.6 ((- 1.3 - 1.3 (6 e^{- 1.3 x}) - 1.3 (9 e^{- 2.6 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.5.2

Multiply $6$ by $- 1.3$ .

$f'' (x) = \frac{93.6 ((- 1.3 - 7.8 e^{- 1.3 x} - 1.3 (9 e^{- 2.6 x})) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.5.3

Multiply $9$ by $- 1.3$ .

$f'' (x) = \frac{93.6 ((- 1.3 - 7.8 e^{- 1.3 x} - 11.7 e^{- 2.6 x}) e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.6

Apply the distributive property.

$f'' (x) = \frac{93.6 (- 1.3 e^{- 1.3 x} - 7.8 e^{- 1.3 x} e^{- 1.3 x} - 11.7 e^{- 2.6 x} e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.7

Simplify.

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Step 1.2.15.3.1.7.1

Multiply $e^{- 1.3 x}$ by $e^{- 1.3 x}$ by adding the exponents.

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Step 1.2.15.3.1.7.1.1

Move $e^{- 1.3 x}$ .

$f'' (x) = \frac{93.6 (- 1.3 e^{- 1.3 x} - 7.8 (e^{- 1.3 x} e^{- 1.3 x}) - 11.7 e^{- 2.6 x} e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.7.1.2

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$f'' (x) = \frac{93.6 (- 1.3 e^{- 1.3 x} - 7.8 e^{- 1.3 x - 1.3 x} - 11.7 e^{- 2.6 x} e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.7.1.3

Subtract $1.3 x$ from $- 1.3 x$ .

$f'' (x) = \frac{93.6 (- 1.3 e^{- 1.3 x} - 7.8 e^{- 2.6 x} - 11.7 e^{- 2.6 x} e^{- 1.3 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.7.2

Multiply $e^{- 2.6 x}$ by $e^{- 1.3 x}$ by adding the exponents.

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Step 1.2.15.3.1.7.2.1

Move $e^{- 1.3 x}$ .

$f'' (x) = \frac{93.6 (- 1.3 e^{- 1.3 x} - 7.8 e^{- 2.6 x} - 11.7 (e^{- 1.3 x} e^{- 2.6 x})) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.7.2.2

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$f'' (x) = \frac{93.6 (- 1.3 e^{- 1.3 x} - 7.8 e^{- 2.6 x} - 11.7 e^{- 1.3 x - 2.6 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.7.2.3

Subtract $2.6 x$ from $- 1.3 x$ .

$f'' (x) = \frac{93.6 (- 1.3 e^{- 1.3 x} - 7.8 e^{- 2.6 x} - 11.7 e^{- 3.9 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.8

Apply the distributive property.

$f'' (x) = \frac{93.6 (- 1.3 e^{- 1.3 x}) + 93.6 (- 7.8 e^{- 2.6 x}) + 93.6 (- 11.7 e^{- 3.9 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.9

Simplify.

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Step 1.2.15.3.1.9.1

Multiply $- 1.3$ by $93.6$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} + 93.6 (- 7.8 e^{- 2.6 x}) + 93.6 (- 11.7 e^{- 3.9 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.9.2

Multiply $- 7.8$ by $93.6$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} + 93.6 (- 11.7 e^{- 3.9 x}) + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.9.3

Multiply $- 11.7$ by $93.6$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 93.6 (7.8 e^{- 2.6 x} \cdot 1) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.10

Multiply $7.8$ by $1$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 93.6 (7.8 e^{- 2.6 x}) + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.11

Multiply $7.8$ by $93.6$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 730.08 e^{- 2.6 x} + 93.6 (7.8 e^{- 2.6 x} (3 e^{- 1.3 x}))}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.12

Multiply $e^{- 2.6 x}$ by $e^{- 1.3 x}$ by adding the exponents.

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Step 1.2.15.3.1.12.1

Move $e^{- 1.3 x}$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 730.08 e^{- 2.6 x} + 93.6 (7.8 (e^{- 1.3 x} e^{- 2.6 x}) \cdot 3)}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.12.2

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 730.08 e^{- 2.6 x} + 93.6 (7.8 e^{- 1.3 x - 2.6 x} \cdot 3)}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.12.3

Subtract $2.6 x$ from $- 1.3 x$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 730.08 e^{- 2.6 x} + 93.6 (7.8 e^{- 3.9 x} \cdot 3)}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.13

Multiply $3$ by $7.8$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 730.08 e^{- 2.6 x} + 93.6 (23.4 e^{- 3.9 x})}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.1.14

Multiply $23.4$ by $93.6$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 730.08 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 730.08 e^{- 2.6 x} + 2190.24 e^{- 3.9 x}}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.2

Add $- 730.08 e^{- 2.6 x}$ and $730.08 e^{- 2.6 x}$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} + 0 e^{- 2.6 x} - 1095.12 e^{- 3.9 x} + 2190.24 e^{- 3.9 x}}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.3

Multiply $0$ by $e^{- 2.6 x}$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} + 0 - 1095.12 e^{- 3.9 x} + 2190.24 e^{- 3.9 x}}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.4

Add $- 121.68 e^{- 1.3 x}$ and $0$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} - 1095.12 e^{- 3.9 x} + 2190.24 e^{- 3.9 x}}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.3.5

Add $- 1095.12 e^{- 3.9 x}$ and $2190.24 e^{- 3.9 x}$ .

$f'' (x) = \frac{- 121.68 e^{- 1.3 x} + 1095.12 e^{- 3.9 x}}{{(1 + 3 e^{- 1.3 x})}^{4}}$

Step 1.2.15.4

Reorder terms.

$f'' (x) = \frac{1095.12 e^{- 3.9 x} - 121.68 e^{- 1.3 x}}{{(3 e^{- 1.3 x} + 1)}^{4}}$

Step 1.2.15.5

Factor $121.68$ out of $1095.12 e^{- 3.9 x} - 121.68 e^{- 1.3 x}$ .

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Step 1.2.15.5.1

Factor $121.68$ out of $1095.12 e^{- 3.9 x}$ .

$f'' (x) = \frac{121.68 (9 e^{- 3.9 x}) - 121.68 e^{- 1.3 x}}{{(3 e^{- 1.3 x} + 1)}^{4}}$

Step 1.2.15.5.2

Factor $121.68$ out of $- 121.68 e^{- 1.3 x}$ .

$f'' (x) = \frac{121.68 (9 e^{- 3.9 x}) + 121.68 (- e^{- 1.3 x})}{{(3 e^{- 1.3 x} + 1)}^{4}}$

Step 1.2.15.5.3

Factor $121.68$ out of $121.68 (9 e^{- 3.9 x}) + 121.68 (- e^{- 1.3 x})$ .

$f'' (x) = \frac{121.68 (9 e^{- 3.9 x} - e^{- 1.3 x})}{{(3 e^{- 1.3 x} + 1)}^{4}}$

Step 1.3

The second derivative of $f (x)$ with respect to $x$ is $\frac{121.68 (9 e^{- 3.9 x} - e^{- 1.3 x})}{{(3 e^{- 1.3 x} + 1)}^{4}}$ .

$\frac{121.68 (9 e^{- 3.9 x} - e^{- 1.3 x})}{{(3 e^{- 1.3 x} + 1)}^{4}}$

Step 2

Set the second derivative equal to $0$ then solve the equation $\frac{121.68 (9 e^{- 3.9 x} - e^{- 1.3 x})}{{(3 e^{- 1.3 x} + 1)}^{4}} = 0$ .

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Step 2.1

Set the second derivative equal to $0$ .

$\frac{121.68 (9 e^{- 3.9 x} - e^{- 1.3 x})}{{(3 e^{- 1.3 x} + 1)}^{4}} = 0$

Step 2.2

Set the numerator equal to zero.

$121.68 (9 e^{- 3.9 x} - e^{- 1.3 x}) = 0$

Step 2.3

Solve the equation for $x$ .

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Step 2.3.1

Divide each term in $121.68 (9 e^{- 3.9 x} - e^{- 1.3 x}) = 0$ by $121.68$ and simplify.

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Step 2.3.1.1

Divide each term in $121.68 (9 e^{- 3.9 x} - e^{- 1.3 x}) = 0$ by $121.68$ .

$\frac{121.68 (9 e^{- 3.9 x} - e^{- 1.3 x})}{121.68} = \frac{0}{121.68}$

Step 2.3.1.2

Simplify the left side.

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Step 2.3.1.2.1

Cancel the common factor of $121.68$ .

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Step 2.3.1.2.1.1

Cancel the common factor.

$\frac{121.68 (9 e^{- 3.9 x} - e^{- 1.3 x})}{121.68} = \frac{0}{121.68}$

Step 2.3.1.2.1.2

Divide $9 e^{- 3.9 x} - e^{- 1.3 x}$ by $1$ .

$9 e^{- 3.9 x} - e^{- 1.3 x} = \frac{0}{121.68}$

Step 2.3.1.3

Simplify the right side.

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Step 2.3.1.3.1

Divide $0$ by $121.68$ .

$9 e^{- 3.9 x} - e^{- 1.3 x} = 0$

Step 2.3.2

Move $- e^{- 1.3 x}$ to the right side of the equation by adding it to both sides.

$9 e^{- 3.9 x} = e^{- 1.3 x}$

Step 2.3.3

Take the natural logarithm of both sides of the equation to remove the variable from the exponent.

$\ln (9 e^{- 3.9 x}) = \ln (e^{- 1.3 x})$

Step 2.3.4

Expand the left side.

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Step 2.3.4.1

Rewrite $\ln (9 e^{- 3.9 x})$ as $\ln (9) + \ln (e^{- 3.9 x})$ .

$\ln (9) + \ln (e^{- 3.9 x}) = \ln (e^{- 1.3 x})$

Step 2.3.4.2

Expand $\ln (e^{- 3.9 x})$ by moving $- 3.9 x$ outside the logarithm.

$\ln (9) - 3.9 x \ln (e) = \ln (e^{- 1.3 x})$

Step 2.3.4.3

The natural logarithm of $e$ is $1$ .

$\ln (9) - 3.9 x \cdot 1 = \ln (e^{- 1.3 x})$

Step 2.3.4.4

Multiply $- 3.9$ by $1$ .

$\ln (9) - 3.9 x = \ln (e^{- 1.3 x})$

Step 2.3.5

Expand the right side.

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Step 2.3.5.1

Expand $\ln (e^{- 1.3 x})$ by moving $- 1.3 x$ outside the logarithm.

$\ln (9) - 3.9 x = - 1.3 x \ln (e)$

Step 2.3.5.2

The natural logarithm of $e$ is $1$ .

$\ln (9) - 3.9 x = - 1.3 x \cdot 1$

Step 2.3.5.3

Multiply $- 1.3$ by $1$ .

$\ln (9) - 3.9 x = - 1.3 x$

Step 2.3.6

Move all terms containing $x$ to the left side of the equation.

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Step 2.3.6.1

Add $1.3 x$ to both sides of the equation.

$\ln (9) - 3.9 x + 1.3 x = 0$

Step 2.3.6.2

Add $- 3.9 x$ and $1.3 x$ .

$\ln (9) - 2.6 x = 0$

Step 2.3.7

Subtract $\ln (9)$ from both sides of the equation.

$- 2.6 x = - \ln (9)$

Step 2.3.8

Divide each term in $- 2.6 x = - \ln (9)$ by $- 2.6$ and simplify.

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Step 2.3.8.1

Divide each term in $- 2.6 x = - \ln (9)$ by $- 2.6$ .

$\frac{- 2.6 x}{- 2.6} = \frac{- \ln (9)}{- 2.6}$

Step 2.3.8.2

Simplify the left side.

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Step 2.3.8.2.1

Cancel the common factor of $- 2.6$ .

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Step 2.3.8.2.1.1

Cancel the common factor.

$\frac{- 2.6 x}{- 2.6} = \frac{- \ln (9)}{- 2.6}$

Step 2.3.8.2.1.2

Divide $x$ by $1$ .

$x = \frac{- \ln (9)}{- 2.6}$

Step 2.3.8.3

Simplify the right side.

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Step 2.3.8.3.1

Dividing two negative values results in a positive value.

$x = \frac{\ln (9)}{2.6}$

Step 2.3.8.3.2

Replace $e$ with an approximation.

$x = \frac{\log_{2.71828182} (9)}{2.6}$

Step 2.3.8.3.3

Log base $2.71828182$ of $9$ is approximately $2.19722457$ .

$x = \frac{2.19722457}{2.6}$

Step 2.3.8.3.4

Divide $2.19722457$ by $2.6$ .

$x = 0.84508637$

Step 3

Find the points where the second derivative is $0$ .

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Step 3.1

Substitute $0.84508637$ in $f (x) = \frac{24}{1 + 3 e^{- 1.3 x}}$ to find the value of $y$ .

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Step 3.1.1

Replace the variable $x$ with $0.84508637$ in the expression.

$f (0.84508637) = \frac{24}{1 + 3 e^{- 1.3 \cdot 0.84508637}}$

Step 3.1.2

Simplify the result.

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Step 3.1.2.1

Simplify the denominator.

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Step 3.1.2.1.1

Multiply $- 1.3$ by $0.84508637$ .

$f (0.84508637) = \frac{24}{1 + 3 e^{- 1.09861228}}$

Step 3.1.2.1.2

Rewrite the expression using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$f (0.84508637) = \frac{24}{1 + 3 (\frac{1}{e^{1.09861228}})}$

Step 3.1.2.1.3

Combine $3$ and $\frac{1}{e^{1.09861228}}$ .

$f (0.84508637) = \frac{24}{1 + \frac{3}{e^{1.09861228}}}$

Step 3.1.2.1.4

Write $1$ as a fraction with a common denominator.

$f (0.84508637) = \frac{24}{\frac{e^{1.09861228}}{e^{1.09861228}} + \frac{3}{e^{1.09861228}}}$

Step 3.1.2.1.5

Combine the numerators over the common denominator.

$f (0.84508637) = \frac{24}{\frac{e^{1.09861228} + 3}{e^{1.09861228}}}$

Step 3.1.2.2

Multiply the numerator by the reciprocal of the denominator.

$f (0.84508637) = 24 (\frac{e^{1.09861228}}{e^{1.09861228} + 3})$

Step 3.1.2.3

Combine $24$ and $\frac{e^{1.09861228}}{e^{1.09861228} + 3}$ .

$f (0.84508637) = \frac{24 e^{1.09861228}}{e^{1.09861228} + 3}$

Step 3.1.2.4

The final answer is $\frac{24 e^{1.09861228}}{e^{1.09861228} + 3}$ .

$\frac{24 e^{1.09861228}}{e^{1.09861228} + 3}$

Step 3.2

The point found by substituting $0.84508637$ in $f (x) = \frac{24}{1 + 3 e^{- 1.3 x}}$ is $(0.84508637, \frac{24 e^{1.09861228}}{e^{1.09861228} + 3})$ . This point can be an inflection point.

$(0.84508637, \frac{24 e^{1.09861228}}{e^{1.09861228} + 3})$

Step 4

Split $(- \infty, \infty)$ into intervals around the points that could potentially be inflection points.

$(- \infty, 0.84508637) \cup (0.84508637, \infty)$

Step 5

Substitute a value from the interval $(- \infty, 0.84508637)$ into the second derivative to determine if it is increasing or decreasing.

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Step 5.1

Replace the variable $x$ with $0.74508637$ in the expression.

$f'' (0.74508637) = \frac{121.68 (9 e^{- 3.9 \cdot 0.74508637} - e^{- 1.3 \cdot 0.74508637})}{{(3 e^{- 1.3 \cdot 0.74508637} + 1)}^{4}}$

Step 5.2

Simplify the result.

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Step 5.2.1

Multiply $121.68$ by $9 e^{- 3.9 \cdot 0.74508637} - e^{- 1.3 \cdot 0.74508637}$ .

$f'' (0.74508637) = \frac{13.71546177}{{(3 e^{- 1.3 \cdot 0.74508637} + 1)}^{4}}$

Step 5.2.2

Simplify the denominator.

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Step 5.2.2.1

Multiply $- 1.3$ by $0.74508637$ .

$f'' (0.74508637) = \frac{13.71546177}{{(3 e^{- 0.96861228} + 1)}^{4}}$

Step 5.2.2.2

Rewrite the expression using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$f'' (0.74508637) = \frac{13.71546177}{{(3 (\frac{1}{e^{0.96861228}}) + 1)}^{4}}$

Step 5.2.2.3

Combine $3$ and $\frac{1}{e^{0.96861228}}$ .

$f'' (0.74508637) = \frac{13.71546177}{{(\frac{3}{e^{0.96861228}} + 1)}^{4}}$

Step 5.2.2.4

Write $1$ as a fraction with a common denominator.

$f'' (0.74508637) = \frac{13.71546177}{{(\frac{3}{e^{0.96861228}} + \frac{e^{0.96861228}}{e^{0.96861228}})}^{4}}$

Step 5.2.2.5

Combine the numerators over the common denominator.

$f'' (0.74508637) = \frac{13.71546177}{{(\frac{3 + e^{0.96861228}}{e^{0.96861228}})}^{4}}$

Step 5.2.2.6

Apply the product rule to $\frac{3 + e^{0.96861228}}{e^{0.96861228}}$ .

$f'' (0.74508637) = \frac{13.71546177}{\frac{{(3 + e^{0.96861228})}^{4}}{{(e^{0.96861228})}^{4}}}$

Step 5.2.2.7

Multiply the exponents in ${(e^{0.96861228})}^{4}$ .

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Step 5.2.2.7.1

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$f'' (0.74508637) = \frac{13.71546177}{\frac{{(3 + e^{0.96861228})}^{4}}{e^{0.96861228 \cdot 4}}}$

Step 5.2.2.7.2

Multiply $0.96861228$ by $4$ .

$f'' (0.74508637) = \frac{13.71546177}{\frac{{(3 + e^{0.96861228})}^{4}}{e^{3.87444915}}}$

Step 5.2.3

Multiply the numerator by the reciprocal of the denominator.

$f'' (0.74508637) = 13.71546177 (\frac{e^{3.87444915}}{{(3 + e^{0.96861228})}^{4}})$

Step 5.2.4

Multiply $13.71546177 \frac{e^{3.87444915}}{{(3 + e^{0.96861228})}^{4}}$ .

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Step 5.2.4.1

Combine $13.71546177$ and $\frac{e^{3.87444915}}{{(3 + e^{0.96861228})}^{4}}$ .

$f'' (0.74508637) = \frac{13.71546177 e^{3.87444915}}{{(3 + e^{0.96861228})}^{4}}$

Step 5.2.4.2

Multiply $13.71546177$ by $e^{3.87444915}$ .

$f'' (0.74508637) = \frac{660.48403172}{{(3 + e^{0.96861228})}^{4}}$

Step 5.2.5

Replace $e$ with an approximation.

$f'' (0.74508637) = \frac{660.48403172}{{(3 + {2.71828182}^{0.96861228})}^{4}}$

Step 5.2.6

Raise $2.71828182$ to the power of $0.96861228$ .

$f'' (0.74508637) = \frac{660.48403172}{{(3 + 2.63428629)}^{4}}$

Step 5.2.7

Add $3$ and $2.63428629$ .

$f'' (0.74508637) = \frac{660.48403172}{{5.63428629}^{4}}$

Step 5.2.8

Raise $5.63428629$ to the power of $4$ .

$f'' (0.74508637) = \frac{660.48403172}{1007.75658204}$

Step 5.2.9

Divide $660.48403172$ by $1007.75658204$ .

$f'' (0.74508637) = 0.65540036$

Step 5.2.10

The final answer is $0.65540036$ .

$0.65540036$

Step 5.3

At $0.74508637$ , the second derivative is $0.65540036$ . Since this is positive, the second derivative is increasing on the interval $(- \infty, 0.84508637)$ .

Increasing on $(- \infty, 0.84508637)$ since $f'' (x) > 0$

Step 6

Substitute a value from the interval $(0.84508637, \infty)$ into the second derivative to determine if it is increasing or decreasing.

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Step 6.1

Replace the variable $x$ with $0.94508637$ in the expression.

$f'' (0.94508637) = \frac{121.68 (9 e^{- 3.9 \cdot 0.94508637} - e^{- 1.3 \cdot 0.94508637})}{{(3 e^{- 1.3 \cdot 0.94508637} + 1)}^{4}}$

Step 6.2

Simplify the result.

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Step 6.2.1

Multiply $121.68$ by $9 e^{- 3.9 \cdot 0.94508637} - e^{- 1.3 \cdot 0.94508637}$ .

$f'' (0.94508637) = \frac{- 8.15412384}{{(3 e^{- 1.3 \cdot 0.94508637} + 1)}^{4}}$

Step 6.2.2

Simplify the denominator.

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Step 6.2.2.1

Multiply $- 1.3$ by $0.94508637$ .

$f'' (0.94508637) = \frac{- 8.15412384}{{(3 e^{- 1.22861228} + 1)}^{4}}$

Step 6.2.2.2

Rewrite the expression using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$f'' (0.94508637) = \frac{- 8.15412384}{{(3 (\frac{1}{e^{1.22861228}}) + 1)}^{4}}$

Step 6.2.2.3

Combine $3$ and $\frac{1}{e^{1.22861228}}$ .

$f'' (0.94508637) = \frac{- 8.15412384}{{(\frac{3}{e^{1.22861228}} + 1)}^{4}}$

Step 6.2.2.4

Write $1$ as a fraction with a common denominator.

$f'' (0.94508637) = \frac{- 8.15412384}{{(\frac{3}{e^{1.22861228}} + \frac{e^{1.22861228}}{e^{1.22861228}})}^{4}}$

Step 6.2.2.5

Combine the numerators over the common denominator.

$f'' (0.94508637) = \frac{- 8.15412384}{{(\frac{3 + e^{1.22861228}}{e^{1.22861228}})}^{4}}$

Step 6.2.2.6

Apply the product rule to $\frac{3 + e^{1.22861228}}{e^{1.22861228}}$ .

$f'' (0.94508637) = \frac{- 8.15412384}{\frac{{(3 + e^{1.22861228})}^{4}}{{(e^{1.22861228})}^{4}}}$

Step 6.2.2.7

Multiply the exponents in ${(e^{1.22861228})}^{4}$ .

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Step 6.2.2.7.1

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$f'' (0.94508637) = \frac{- 8.15412384}{\frac{{(3 + e^{1.22861228})}^{4}}{e^{1.22861228 \cdot 4}}}$

Step 6.2.2.7.2

Multiply $1.22861228$ by $4$ .

$f'' (0.94508637) = \frac{- 8.15412384}{\frac{{(3 + e^{1.22861228})}^{4}}{e^{4.91444915}}}$

Step 6.2.3

Multiply the numerator by the reciprocal of the denominator.

$f'' (0.94508637) = - 8.15412384 \frac{e^{4.91444915}}{{(3 + e^{1.22861228})}^{4}}$

Step 6.2.4

Multiply $- 8.15412384 \frac{e^{4.91444915}}{{(3 + e^{1.22861228})}^{4}}$ .

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Step 6.2.4.1

Combine $- 8.15412384$ and $\frac{e^{4.91444915}}{{(3 + e^{1.22861228})}^{4}}$ .

$f'' (0.94508637) = \frac{- 8.15412384 e^{4.91444915}}{{(3 + e^{1.22861228})}^{4}}$

Step 6.2.4.2

Multiply $- 8.15412384$ by $e^{4.91444915}$ .

$f'' (0.94508637) = \frac{- 1110.95240355}{{(3 + e^{1.22861228})}^{4}}$

Step 6.2.5

Move the negative in front of the fraction.

$f'' (0.94508637) = - \frac{1110.95240355}{{(3 + e^{1.22861228})}^{4}}$

Step 6.2.6

Replace $e$ with an approximation.

$f'' (0.94508637) = - \frac{1110.95240355}{{(3 + {2.71828182}^{1.22861228})}^{4}}$

Step 6.2.7

Raise $2.71828182$ to the power of $1.22861228$ .

$f'' (0.94508637) = - \frac{1110.95240355}{{(3 + 3.41648514)}^{4}}$

Step 6.2.8

Add $3$ and $3.41648514$ .

$f'' (0.94508637) = - \frac{1110.95240355}{{6.41648514}^{4}}$

Step 6.2.9

Raise $6.41648514$ to the power of $4$ .

$f'' (0.94508637) = - \frac{1110.95240355}{1695.07443516}$

Step 6.2.10

Divide $1110.95240355$ by $1695.07443516$ .

$f'' (0.94508637) = - 1 \cdot 0.65540036$

Step 6.2.11

Multiply $- 1$ by $0.65540036$ .

$f'' (0.94508637) = - 0.65540036$

Step 6.2.12

The final answer is $- 0.65540036$ .

$- 0.65540036$

Step 6.3

At $0.94508637$ , the second derivative is $- 0.65540036$ . Since this is negative, the second derivative is decreasing on the interval $(0.84508637, \infty)$

Decreasing on $(0.84508637, \infty)$ since $f'' (x) < 0$

Step 7

An inflection point is a point on a curve at which the concavity changes sign from plus to minus or from minus to plus. The inflection point in this case is $(0.84508637, \frac{24 e^{1.09861228}}{e^{1.09861228} + 3})$ .

$(0.84508637, \frac{24 e^{1.09861228}}{e^{1.09861228} + 3})$

Step 8