Calculus Examples

$\sin (4 x) \cos^{2} (x)$

Step 1

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 $f (x) = \sin (4 x)$ and $g (x) = \cos^{2} (x)$ .

$\sin (4 x) \frac{d}{d x} [\cos^{2} (x)] + \cos^{2} (x) \frac{d}{d x} [\sin (4 x)]$

Step 2

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

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Step 2.1

To apply the Chain Rule, set $u_{1}$ as $\cos (x)$ .

$\sin (4 x) (\frac{d}{d u_{1}} [{u_{1}}^{2}] \frac{d}{d x} [\cos (x)]) + \cos^{2} (x) \frac{d}{d x} [\sin (4 x)]$

Step 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 $n = 2$ .

$\sin (4 x) (2 u_{1} \frac{d}{d x} [\cos (x)]) + \cos^{2} (x) \frac{d}{d x} [\sin (4 x)]$

Step 2.3

Replace all occurrences of $u_{1}$ with $\cos (x)$ .

$\sin (4 x) (2 \cos (x) \frac{d}{d x} [\cos (x)]) + \cos^{2} (x) \frac{d}{d x} [\sin (4 x)]$

Step 3

Move $2$ to the left of $\sin (4 x)$ .

$2 \cdot \sin (4 x) \cos (x) \frac{d}{d x} [\cos (x)] + \cos^{2} (x) \frac{d}{d x} [\sin (4 x)]$

Step 4

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

$2 \sin (4 x) \cos (x) (- \sin (x)) + \cos^{2} (x) \frac{d}{d x} [\sin (4 x)]$

Step 5

Multiply $- 1$ by $2$ .

$- 2 \sin (4 x) \cos (x) \sin (x) + \cos^{2} (x) \frac{d}{d x} [\sin (4 x)]$

Step 6

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sin (x)$ and $g (x) = 4 x$ .

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Step 6.1

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

$- 2 \sin (4 x) \cos (x) \sin (x) + \cos^{2} (x) (\frac{d}{d u_{2}} [\sin (u_{2})] \frac{d}{d x} [4 x])$

Step 6.2

The derivative of $\sin (u_{2})$ with respect to $u_{2}$ is $\cos (u_{2})$ .

$- 2 \sin (4 x) \cos (x) \sin (x) + \cos^{2} (x) (\cos (u_{2}) \frac{d}{d x} [4 x])$

Step 6.3

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

$- 2 \sin (4 x) \cos (x) \sin (x) + \cos^{2} (x) (\cos (4 x) \frac{d}{d x} [4 x])$

Step 7

Differentiate.

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Step 7.1

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

$- 2 \sin (4 x) \cos (x) \sin (x) + \cos^{2} (x) \cos (4 x) (4 \frac{d}{d x} [x])$

Step 7.2

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

$- 2 \sin (4 x) \cos (x) \sin (x) + \cos^{2} (x) \cos (4 x) (4 \cdot 1)$

Step 7.3

Simplify the expression.

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Step 7.3.1

Multiply $4$ by $1$ .

$- 2 \sin (4 x) \cos (x) \sin (x) + \cos^{2} (x) \cos (4 x) \cdot 4$

Step 7.3.2

Move $4$ to the left of $\cos^{2} (x) \cos (4 x)$ .

$- 2 \sin (4 x) \cos (x) \sin (x) + 4 \cdot (\cos^{2} (x) \cos (4 x))$

Step 7.3.3

Reorder terms.

$- 2 \cos (x) \sin (x) \sin (4 x) + 4 \cos^{2} (x) \cos (4 x)$