Calculus Examples

$(4 x^{2} + 8 x) \cos (x)$

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 $f (x) = 4 x^{2} + 8 x$ and $g (x) = \cos (x)$ .

$(4 x^{2} + 8 x) \frac{d}{d x} [\cos (x)] + \cos (x) \frac{d}{d x} [4 x^{2} + 8 x]$

Step 2

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

$(4 x^{2} + 8 x) (- \sin (x)) + \cos (x) \frac{d}{d x} [4 x^{2} + 8 x]$

Step 3

Differentiate.

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Step 3.1

By the Sum Rule, the derivative of $4 x^{2} + 8 x$ with respect to $x$ is $\frac{d}{d x} [4 x^{2}] + \frac{d}{d x} [8 x]$ .

$(4 x^{2} + 8 x) (- \sin (x)) + \cos (x) (\frac{d}{d x} [4 x^{2}] + \frac{d}{d x} [8 x])$

Step 3.2

Since $4$ is constant with respect to $x$ , the derivative of $4 x^{2}$ with respect to $x$ is $4 \frac{d}{d x} [x^{2}]$ .

$(4 x^{2} + 8 x) (- \sin (x)) + \cos (x) (4 \frac{d}{d x} [x^{2}] + \frac{d}{d x} [8 x])$

Step 3.3

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

$(4 x^{2} + 8 x) (- \sin (x)) + \cos (x) (4 (2 x) + \frac{d}{d x} [8 x])$

Step 3.4

Multiply $2$ by $4$ .

$(4 x^{2} + 8 x) (- \sin (x)) + \cos (x) (8 x + \frac{d}{d x} [8 x])$

Step 3.5

Since $8$ is constant with respect to $x$ , the derivative of $8 x$ with respect to $x$ is $8 \frac{d}{d x} [x]$ .

$(4 x^{2} + 8 x) (- \sin (x)) + \cos (x) (8 x + 8 \frac{d}{d x} [x])$

Step 3.6

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

$(4 x^{2} + 8 x) (- \sin (x)) + \cos (x) (8 x + 8 \cdot 1)$

Step 3.7

Multiply $8$ by $1$ .

$(4 x^{2} + 8 x) (- \sin (x)) + \cos (x) (8 x + 8)$

Step 4

Simplify.

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Step 4.1

Apply the distributive property.

$4 x^{2} (- \sin (x)) + 8 x (- \sin (x)) + \cos (x) (8 x + 8)$

Step 4.2

Apply the distributive property.

$4 x^{2} (- \sin (x)) + 8 x (- \sin (x)) + \cos (x) (8 x) + \cos (x) \cdot 8$

Step 4.3

Combine terms.

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Step 4.3.1

Multiply $- 1$ by $4$ .

$- 4 x^{2} \sin (x) + 8 x (- \sin (x)) + \cos (x) (8 x) + \cos (x) \cdot 8$

Step 4.3.2

Multiply $- 1$ by $8$ .

$- 4 x^{2} \sin (x) - 8 x \sin (x) + \cos (x) (8 x) + \cos (x) \cdot 8$

Step 4.3.3

Move $8$ to the left of $\cos (x)$ .

$- 4 x^{2} \sin (x) - 8 x \sin (x) + \cos (x) (8 x) + 8 \cos (x)$

Step 4.4

Reorder terms.

$- 4 x^{2} \sin (x) - 8 x \sin (x) + 8 x \cos (x) + 8 \cos (x)$