Calculus Examples

$lim_{x \to - \infty} (x^{2} - x^{3}) e^{2 x}$

Step 1

Rewrite $(x^{2} - x^{3}) e^{2 x}$ as $\frac{x^{2} - x^{3}}{e^{- 2 x}}$ .

$lim_{x \to - \infty} \frac{x^{2} - x^{3}}{e^{- 2 x}}$

Step 2

Apply L'Hospital's rule.

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Step 2.1

Evaluate the limit of the numerator and the limit of the denominator.

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Step 2.1.1

Take the limit of the numerator and the limit of the denominator.

$\frac{lim_{x \to - \infty} x^{2} - x^{3}}{lim_{x \to - \infty} e^{- 2 x}}$

Step 2.1.2

Evaluate the limit of the numerator.

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Step 2.1.2.1

Reorder $x^{2}$ and $- x^{3}$ .

$\frac{lim_{x \to - \infty} - x^{3} + x^{2}}{lim_{x \to - \infty} e^{- 2 x}}$

Step 2.1.2.2

The limit at negative infinity of a polynomial of odd degree whose leading coefficient is negative is infinity.

$\frac{\infty}{lim_{x \to - \infty} e^{- 2 x}}$

Step 2.1.3

Since the exponent $- 2 x$ approaches $\infty$ , the quantity $e^{- 2 x}$ approaches $\infty$ .

$\frac{\infty}{\infty}$

Step 2.1.4

Infinity divided by infinity is undefined.

Undefined

$\frac{\infty}{\infty}$

Step 2.2

Since $\frac{\infty}{\infty}$ is of indeterminate form, apply L'Hospital's Rule. L'Hospital's Rule states that the limit of a quotient of functions is equal to the limit of the quotient of their derivatives.

$lim_{x \to - \infty} \frac{x^{2} - x^{3}}{e^{- 2 x}} = lim_{x \to - \infty} \frac{\frac{d}{d x} [x^{2} - x^{3}]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 2.3

Find the derivative of the numerator and denominator.

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Step 2.3.1

Differentiate the numerator and denominator.

$lim_{x \to - \infty} \frac{\frac{d}{d x} [x^{2} - x^{3}]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 2.3.2

By the Sum Rule, the derivative of $x^{2} - x^{3}$ with respect to $x$ is $\frac{d}{d x} [x^{2}] + \frac{d}{d x} [- x^{3}]$ .

$lim_{x \to - \infty} \frac{\frac{d}{d x} [x^{2}] + \frac{d}{d x} [- x^{3}]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 2.3.3

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

$lim_{x \to - \infty} \frac{2 x + \frac{d}{d x} [- x^{3}]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 2.3.4

Evaluate $\frac{d}{d x} [- x^{3}]$ .

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Step 2.3.4.1

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

$lim_{x \to - \infty} \frac{2 x - \frac{d}{d x} [x^{3}]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 2.3.4.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 3$ .

$lim_{x \to - \infty} \frac{2 x - (3 x^{2})}{\frac{d}{d x} [e^{- 2 x}]}$

Step 2.3.4.3

Multiply $3$ by $- 1$ .

$lim_{x \to - \infty} \frac{2 x - 3 x^{2}}{\frac{d}{d x} [e^{- 2 x}]}$

Step 2.3.5

Reorder terms.

$lim_{x \to - \infty} \frac{- 3 x^{2} + 2 x}{\frac{d}{d x} [e^{- 2 x}]}$

Step 2.3.6

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

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Step 2.3.6.1

To apply the Chain Rule, set $u$ as $- 2 x$ .

$lim_{x \to - \infty} \frac{- 3 x^{2} + 2 x}{\frac{d}{d u} [e^{u}] \frac{d}{d x} [- 2 x]}$

Step 2.3.6.2

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

$lim_{x \to - \infty} \frac{- 3 x^{2} + 2 x}{e^{u} \frac{d}{d x} [- 2 x]}$

Step 2.3.6.3

Replace all occurrences of $u$ with $- 2 x$ .

$lim_{x \to - \infty} \frac{- 3 x^{2} + 2 x}{e^{- 2 x} \frac{d}{d x} [- 2 x]}$

Step 2.3.7

Since $- 2$ is constant with respect to $x$ , the derivative of $- 2 x$ with respect to $x$ is $- 2 \frac{d}{d x} [x]$ .

$lim_{x \to - \infty} \frac{- 3 x^{2} + 2 x}{e^{- 2 x} (- 2 \frac{d}{d x} [x])}$

Step 2.3.8

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

$lim_{x \to - \infty} \frac{- 3 x^{2} + 2 x}{e^{- 2 x} (- 2 \cdot 1)}$

Step 2.3.9

Multiply $- 2$ by $1$ .

$lim_{x \to - \infty} \frac{- 3 x^{2} + 2 x}{e^{- 2 x} \cdot - 2}$

Step 2.3.10

Move $- 2$ to the left of $e^{- 2 x}$ .

$lim_{x \to - \infty} \frac{- 3 x^{2} + 2 x}{- 2 e^{- 2 x}}$

Step 2.4

Factor $x$ out of $- 3 x^{2} + 2 x$ .

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Step 2.4.1

Factor $x$ out of $- 3 x^{2}$ .

$lim_{x \to - \infty} \frac{x (- 3 x) + 2 x}{- 2 e^{- 2 x}}$

Step 2.4.2

Factor $x$ out of $2 x$ .

$lim_{x \to - \infty} \frac{x (- 3 x) + x \cdot 2}{- 2 e^{- 2 x}}$

Step 2.4.3

Factor $x$ out of $x (- 3 x) + x \cdot 2$ .

$lim_{x \to - \infty} \frac{x (- 3 x + 2)}{- 2 e^{- 2 x}}$

Step 2.5

Move the negative in front of the fraction.

$lim_{x \to - \infty} - \frac{x (- 3 x + 2)}{(2) e^{- 2 x}}$

Step 2.6

Factor $- 1$ out of $- 3 x$ .

$lim_{x \to - \infty} - \frac{x (- (3 x) + 2)}{2 e^{- 2 x}}$

Step 2.7

Rewrite $2$ as $- 1 (- 2)$ .

$lim_{x \to - \infty} - \frac{x (- (3 x) - 1 (- 2))}{2 e^{- 2 x}}$

Step 2.8

Factor $- 1$ out of $- (3 x) - 1 (- 2)$ .

$lim_{x \to - \infty} - \frac{x (- (3 x - 2))}{2 e^{- 2 x}}$

Step 2.9

Rewrite $- (3 x - 2)$ as $- 1 (3 x - 2)$ .

$lim_{x \to - \infty} - \frac{x (- 1 (3 x - 2))}{2 e^{- 2 x}}$

Step 2.10

Move the negative in front of the fraction.

$lim_{x \to - \infty} - - \frac{x (3 x - 2)}{2 e^{- 2 x}}$

Step 2.11

Multiply $- 1$ by $- 1$ .

$lim_{x \to - \infty} 1 \frac{x (3 x - 2)}{2 e^{- 2 x}}$

Step 2.12

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

$lim_{x \to - \infty} \frac{x (3 x - 2)}{2 e^{- 2 x}}$

Step 3

Move the term $\frac{1}{2}$ outside of the limit because it is constant with respect to $x$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{x (3 x - 2)}{e^{- 2 x}}$

Step 4

Apply L'Hospital's rule.

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Step 4.1

Evaluate the limit of the numerator and the limit of the denominator.

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Step 4.1.1

Take the limit of the numerator and the limit of the denominator.

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} x (3 x - 2)}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.2

Evaluate the limit of the numerator.

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Step 4.1.2.1

Apply the distributive property.

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} x \cdot 3 x + x \cdot - 2}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.2.2

Simplify with commuting.

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Step 4.1.2.2.1

Reorder $x$ and $3$ .

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} 3 \cdot x \cdot x + x \cdot - 2}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.2.2.2

Reorder $x$ and $- 2$ .

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} 3 \cdot x \cdot x - 2 \cdot x}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.2.3

Raise $x$ to the power of $1$ .

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} 3 x^{1} x - 2 x}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.2.4

Raise $x$ to the power of $1$ .

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} 3 x^{1} x^{1} - 2 x}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.2.5

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

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} 3 x^{1 + 1} - 2 x}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.2.6

Add $1$ and $1$ .

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} 3 x^{2} - 2 x}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.2.7

The limit at negative infinity of a polynomial of even degree whose leading coefficient is positive is infinity.

$\frac{1}{2} \cdot \frac{\infty}{lim_{x \to - \infty} e^{- 2 x}}$

Step 4.1.3

Since the exponent $- 2 x$ approaches $\infty$ , the quantity $e^{- 2 x}$ approaches $\infty$ .

$\frac{1}{2} \cdot \frac{\infty}{\infty}$

Step 4.1.4

Infinity divided by infinity is undefined.

Undefined

$\frac{1}{2} \cdot \frac{\infty}{\infty}$

Step 4.2

$lim_{x \to - \infty} \frac{x (3 x - 2)}{e^{- 2 x}} = lim_{x \to - \infty} \frac{\frac{d}{d x} [x (3 x - 2)]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3

Find the derivative of the numerator and denominator.

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Step 4.3.1

Differentiate the numerator and denominator.

$\frac{1}{2} lim_{x \to - \infty} \frac{\frac{d}{d x} [x (3 x - 2)]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.2

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

$\frac{1}{2} lim_{x \to - \infty} \frac{x \frac{d}{d x} [3 x - 2] + (3 x - 2) \frac{d}{d x} [x]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.3

By the Sum Rule, the derivative of $3 x - 2$ with respect to $x$ is $\frac{d}{d x} [3 x] + \frac{d}{d x} [- 2]$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{x (\frac{d}{d x} [3 x] + \frac{d}{d x} [- 2]) + (3 x - 2) \frac{d}{d x} [x]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.4

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

$\frac{1}{2} lim_{x \to - \infty} \frac{x (3 \frac{d}{d x} [x] + \frac{d}{d x} [- 2]) + (3 x - 2) \frac{d}{d x} [x]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.5

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

$\frac{1}{2} lim_{x \to - \infty} \frac{x (3 \cdot 1 + \frac{d}{d x} [- 2]) + (3 x - 2) \frac{d}{d x} [x]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.6

Multiply $3$ by $1$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{x (3 + \frac{d}{d x} [- 2]) + (3 x - 2) \frac{d}{d x} [x]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.7

Since $- 2$ is constant with respect to $x$ , the derivative of $- 2$ with respect to $x$ is $0$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{x (3 + 0) + (3 x - 2) \frac{d}{d x} [x]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.8

Add $3$ and $0$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{x \cdot 3 + (3 x - 2) \frac{d}{d x} [x]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.9

Move $3$ to the left of $x$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3 \cdot x + (3 x - 2) \frac{d}{d x} [x]}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.10

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

$\frac{1}{2} lim_{x \to - \infty} \frac{3 x + (3 x - 2) \cdot 1}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.11

Multiply $3 x - 2$ by $1$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3 x + 3 x - 2}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.12

Add $3 x$ and $3 x$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{6 x - 2}{\frac{d}{d x} [e^{- 2 x}]}$

Step 4.3.13

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 $g (x) = - 2 x$ .

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Step 4.3.13.1

To apply the Chain Rule, set $u$ as $- 2 x$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{6 x - 2}{\frac{d}{d u} [e^{u}] \frac{d}{d x} [- 2 x]}$

Step 4.3.13.2

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

$\frac{1}{2} lim_{x \to - \infty} \frac{6 x - 2}{e^{u} \frac{d}{d x} [- 2 x]}$

Step 4.3.13.3

Replace all occurrences of $u$ with $- 2 x$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{6 x - 2}{e^{- 2 x} \frac{d}{d x} [- 2 x]}$

Step 4.3.14

Since $- 2$ is constant with respect to $x$ , the derivative of $- 2 x$ with respect to $x$ is $- 2 \frac{d}{d x} [x]$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{6 x - 2}{e^{- 2 x} \cdot - 2 \frac{d}{d x} [x]}$

Step 4.3.15

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

$\frac{1}{2} lim_{x \to - \infty} \frac{6 x - 2}{e^{- 2 x} \cdot - 2 \cdot 1}$

Step 4.3.16

Multiply $- 2$ by $1$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{6 x - 2}{e^{- 2 x} \cdot - 2}$

Step 4.3.17

Move $- 2$ to the left of $e^{- 2 x}$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{6 x - 2}{- 2 e^{- 2 x}}$

Step 4.4

Cancel the common factor of $6 x - 2$ and $- 2$ .

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Step 4.4.1

Factor $2$ out of $6 x$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{2 \cdot 3 x - 2}{- 2 e^{- 2 x}}$

Step 4.4.2

Factor $2$ out of $- 2$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{2 \cdot 3 x + 2 (- 1)}{- 2 e^{- 2 x}}$

Step 4.4.3

Factor $2$ out of $2 (3 x) + 2 (- 1)$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{2 (3 x - 1)}{- 2 e^{- 2 x}}$

Step 4.4.4

Cancel the common factors.

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Step 4.4.4.1

Factor $2$ out of $- 2 e^{- 2 x}$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{2 (3 x - 1)}{2 \cdot - 1 e^{- 2 x}}$

Step 4.4.4.2

Cancel the common factor.

$\frac{1}{2} lim_{x \to - \infty} \frac{2 (3 x - 1)}{2 \cdot - 1 e^{- 2 x}}$

Step 4.4.4.3

Rewrite the expression.

$\frac{1}{2} lim_{x \to - \infty} \frac{3 x - 1}{- e^{- 2 x}}$

Step 5

Apply L'Hospital's rule.

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Step 5.1

Evaluate the limit of the numerator and the limit of the denominator.

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Step 5.1.1

Take the limit of the numerator and the limit of the denominator.

$\frac{1}{2} \cdot \frac{lim_{x \to - \infty} 3 x - 1}{lim_{x \to - \infty} - e^{- 2 x}}$

Step 5.1.2

The limit at negative infinity of a polynomial of odd degree whose leading coefficient is positive is negative infinity.

$\frac{1}{2} \cdot \frac{- \infty}{lim_{x \to - \infty} - e^{- 2 x}}$

Step 5.1.3

Since the function $e^{- 2 x}$ approaches $\infty$ , the negative constant $- 1$ times the function approaches $- \infty$ .

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Step 5.1.3.1

Consider the limit with the constant multiple $- 1$ removed.

$\frac{1}{2} \cdot \frac{- \infty}{lim_{x \to - \infty} e^{- 2 x}}$

Step 5.1.3.2

Since the exponent $- 2 x$ approaches $\infty$ , the quantity $e^{- 2 x}$ approaches $\infty$ .

$\frac{1}{2} \cdot \frac{- \infty}{\infty}$

Step 5.1.3.3

Since the function $e^{- 2 x}$ approaches $\infty$ , the negative constant $- 1$ times the function approaches $- \infty$ .

$\frac{1}{2} \cdot \frac{- \infty}{- \infty}$

Step 5.1.3.4

Infinity divided by infinity is undefined.

Undefined

$\frac{1}{2} \cdot \frac{- \infty}{- \infty}$

Step 5.1.4

Infinity divided by infinity is undefined.

Undefined

$\frac{1}{2} \cdot \frac{- \infty}{- \infty}$

Step 5.2

Since $\frac{- \infty}{- \infty}$ is of indeterminate form, apply L'Hospital's Rule. L'Hospital's Rule states that the limit of a quotient of functions is equal to the limit of the quotient of their derivatives.

$lim_{x \to - \infty} \frac{3 x - 1}{- e^{- 2 x}} = lim_{x \to - \infty} \frac{\frac{d}{d x} [3 x - 1]}{\frac{d}{d x} [- e^{- 2 x}]}$

Step 5.3

Find the derivative of the numerator and denominator.

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Step 5.3.1

Differentiate the numerator and denominator.

$\frac{1}{2} lim_{x \to - \infty} \frac{\frac{d}{d x} [3 x - 1]}{\frac{d}{d x} [- e^{- 2 x}]}$

Step 5.3.2

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

$\frac{1}{2} lim_{x \to - \infty} \frac{\frac{d}{d x} [3 x] + \frac{d}{d x} [- 1]}{\frac{d}{d x} [- e^{- 2 x}]}$

Step 5.3.3

Evaluate $\frac{d}{d x} [3 x]$ .

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Step 5.3.3.1

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

$\frac{1}{2} lim_{x \to - \infty} \frac{3 \frac{d}{d x} [x] + \frac{d}{d x} [- 1]}{\frac{d}{d x} [- e^{- 2 x}]}$

Step 5.3.3.2

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

$\frac{1}{2} lim_{x \to - \infty} \frac{3 \cdot 1 + \frac{d}{d x} [- 1]}{\frac{d}{d x} [- e^{- 2 x}]}$

Step 5.3.3.3

Multiply $3$ by $1$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3 + \frac{d}{d x} [- 1]}{\frac{d}{d x} [- e^{- 2 x}]}$

Step 5.3.4

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

$\frac{1}{2} lim_{x \to - \infty} \frac{3 + 0}{\frac{d}{d x} [- e^{- 2 x}]}$

Step 5.3.5

Add $3$ and $0$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{\frac{d}{d x} [- e^{- 2 x}]}$

Step 5.3.6

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

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{- \frac{d}{d x} [e^{- 2 x}]}$

Step 5.3.7

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 $g (x) = - 2 x$ .

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Step 5.3.7.1

To apply the Chain Rule, set $u$ as $- 2 x$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{- \frac{d}{d u} [e^{u}] \frac{d}{d x} [- 2 x]}$

Step 5.3.7.2

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

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{- e^{u} \frac{d}{d x} [- 2 x]}$

Step 5.3.7.3

Replace all occurrences of $u$ with $- 2 x$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{- e^{- 2 x} \frac{d}{d x} [- 2 x]}$

Step 5.3.8

Since $- 2$ is constant with respect to $x$ , the derivative of $- 2 x$ with respect to $x$ is $- 2 \frac{d}{d x} [x]$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{- e^{- 2 x} \cdot - 2 \frac{d}{d x} [x]}$

Step 5.3.9

Multiply $- 2$ by $- 1$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{2 e^{- 2 x} \frac{d}{d x} [x]}$

Step 5.3.10

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

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{2 e^{- 2 x} \cdot 1}$

Step 5.3.11

Multiply $2$ by $1$ .

$\frac{1}{2} lim_{x \to - \infty} \frac{3}{2 e^{- 2 x}}$

Step 6

Move the term $\frac{3}{2}$ outside of the limit because it is constant with respect to $x$ .

$\frac{1}{2} \cdot \frac{3}{2} lim_{x \to - \infty} \frac{1}{e^{- 2 x}}$

Step 7

Since its numerator approaches a real number while its denominator is unbounded, the fraction $\frac{1}{e^{- 2 x}}$ approaches $0$ .

$\frac{1}{2} \cdot \frac{3}{2} \cdot 0$

Step 8

Simplify the answer.

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Step 8.1

Multiply $\frac{1}{2} \cdot \frac{3}{2}$ .

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Step 8.1.1

Multiply $\frac{1}{2}$ by $\frac{3}{2}$ .

$\frac{3}{2 \cdot 2} \cdot 0$

Step 8.1.2

Multiply $2$ by $2$ .

$\frac{3}{4} \cdot 0$

Step 8.2

Multiply $\frac{3}{4}$ by $0$ .

$0$