Calculus Examples

$y = e^{4 x} \sin (x)$

Step 1

Find the first derivative.

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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 $f (x) = e^{4 x}$ and $g (x) = \sin (x)$ .

$f' (x) = e^{4 x} \frac{d}{d x} (\sin (x)) + \sin (x) \frac{d}{d x} (e^{4 x})$

The derivative of $\sin (x)$ with respect to $x$ is $\cos (x)$ .

$f' (x) = e^{4 x} \cos (x) + \sin (x) \frac{d}{d x} (e^{4 x})$

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 $g (x) = 4 x$ .

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To apply the Chain Rule, set $u$ as $4 x$ .

$f' (x) = e^{4 x} \cos (x) + \sin (x) (\frac{d}{d u} (e^{u}) \frac{d}{d x} (4 x))$

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

$f' (x) = e^{4 x} \cos (x) + \sin (x) (e^{u} \frac{d}{d x} (4 x))$

Replace all occurrences of $u$ with $4 x$ .

$f' (x) = e^{4 x} \cos (x) + \sin (x) (e^{4 x} \frac{d}{d x} (4 x))$

Differentiate.

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Since $4$ is constant with respect to $x$ , the derivative of $4 x$ with respect to $x$ is $4 \frac{d}{d x} [x]$ .

$f' (x) = e^{4 x} \cos (x) + \sin (x) (e^{4 x} (4 \frac{d}{d x} (x)))$

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

$f' (x) = e^{4 x} \cos (x) + \sin (x) (e^{4 x} (4 \cdot 1))$

Simplify the expression.

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Multiply $4$ by $1$ .

$f' (x) = e^{4 x} \cos (x) + \sin (x) (e^{4 x} \cdot 4)$

Move $4$ to the left of $e^{4 x}$ .

$f' (x) = e^{4 x} \cos (x) + \sin (x) (4 \cdot e^{4 x})$

Reorder terms.

$f' (x) = e^{4 x} \cos (x) + 4 e^{4 x} \sin (x)$

Step 2

Find the second derivative.

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By the Sum Rule, the derivative of $e^{4 x} \cos (x) + 4 e^{4 x} \sin (x)$ with respect to $x$ is $\frac{d}{d x} [e^{4 x} \cos (x)] + \frac{d}{d x} [4 e^{4 x} \sin (x)]$ .

$f'' (x) = \frac{d}{d x} (e^{4 x} \cos (x)) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

Evaluate $\frac{d}{d x} [e^{4 x} \cos (x)]$ .

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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 $f (x) = e^{4 x}$ and $g (x) = \cos (x)$ .

$f'' (x) = e^{4 x} \frac{d}{d x} (\cos (x)) + \cos (x) \frac{d}{d x} (e^{4 x}) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

The derivative of $\cos (x)$ with respect to $x$ is $- \sin (x)$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) \frac{d}{d x} (e^{4 x}) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

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 $g (x) = 4 x$ .

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To apply the Chain Rule, set $u_{1}$ as $4 x$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (\frac{d}{d u (1)} (e^{u_{1}}) \frac{d}{d x} (4 x)) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

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

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (e^{u_{1}} \frac{d}{d x} (4 x)) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

Replace all occurrences of $u_{1}$ with $4 x$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (e^{4 x} \frac{d}{d x} (4 x)) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

Since $4$ is constant with respect to $x$ , the derivative of $4 x$ with respect to $x$ is $4 \frac{d}{d x} [x]$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (e^{4 x} (4 \frac{d}{d x} (x))) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

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

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (e^{4 x} (4 \cdot 1)) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

Multiply $4$ by $1$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (e^{4 x} \cdot 4) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

Move $4$ to the left of $e^{4 x}$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + \frac{d}{d x} (4 e^{4 x} \sin (x))$

Evaluate $\frac{d}{d x} [4 e^{4 x} \sin (x)]$ .

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Since $4$ is constant with respect to $x$ , the derivative of $4 e^{4 x} \sin (x)$ with respect to $x$ is $4 \frac{d}{d x} [e^{4 x} \sin (x)]$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 \frac{d}{d x} (e^{4 x} \sin (x))$

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 $f (x) = e^{4 x}$ and $g (x) = \sin (x)$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \frac{d}{d x} (\sin (x)) + \sin (x) \frac{d}{d x} (e^{4 x}))$

The derivative of $\sin (x)$ with respect to $x$ is $\cos (x)$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x) + \sin (x) \frac{d}{d x} (e^{4 x}))$

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 $g (x) = 4 x$ .

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To apply the Chain Rule, set $u_{2}$ as $4 x$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x) + \sin (x) (\frac{d}{d u (2)} (e^{u_{2}}) \frac{d}{d x} (4 x)))$

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

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x) + \sin (x) (e^{u_{2}} \frac{d}{d x} (4 x)))$

Replace all occurrences of $u_{2}$ with $4 x$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x) + \sin (x) (e^{4 x} \frac{d}{d x} (4 x)))$

Since $4$ is constant with respect to $x$ , the derivative of $4 x$ with respect to $x$ is $4 \frac{d}{d x} [x]$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x) + \sin (x) (e^{4 x} (4 \frac{d}{d x} (x))))$

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

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x) + \sin (x) (e^{4 x} (4 \cdot 1)))$

Multiply $4$ by $1$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x) + \sin (x) (e^{4 x} \cdot 4))$

Move $4$ to the left of $e^{4 x}$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x) + \sin (x) (4 e^{4 x}))$

Simplify.

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Apply the distributive property.

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 (e^{4 x} \cos (x)) + 4 (\sin (x) (4 e^{4 x}))$

Combine terms.

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Multiply $4$ by $4$ .

$f'' (x) = e^{4 x} (- \sin (x)) + \cos (x) (4 e^{4 x}) + 4 e^{4 x} \cos (x) + 16 (\sin (x) (e^{4 x}))$

Add $\cos (x) (4 e^{4 x})$ and $4 e^{4 x} \cos (x)$ .

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Move $\cos (x)$ .

$f'' (x) = e^{4 x} (- \sin (x)) + 4 e^{4 x} \cos (x) + 4 e^{4 x} \cos (x) + 16 \sin (x) e^{4 x}$

Add $4 e^{4 x} \cos (x)$ and $4 e^{4 x} \cos (x)$ .

$f'' (x) = e^{4 x} (- \sin (x)) + 8 e^{4 x} \cos (x) + 16 \sin (x) e^{4 x}$

Move $\sin (x)$ .

$f'' (x) = - 1 \cdot (e^{4 x} \sin (x)) + 16 e^{4 x} \sin (x) + 8 e^{4 x} \cos (x)$

Rewrite $- 1 e^{4 x}$ as $- e^{4 x}$ .

$f'' (x) = - e^{4 x} \sin (x) + 16 e^{4 x} \sin (x) + 8 e^{4 x} \cos (x)$

Add $- e^{4 x} \sin (x)$ and $16 e^{4 x} \sin (x)$ .

$f'' (x) = 15 e^{4 x} \sin (x) + 8 e^{4 x} \cos (x)$