Calculus Examples

$y = x^{3} \cos (x) - 8 x \sin (x) - 8 \cos (x)$

Step 1

By the Sum Rule, the derivative of $x^{3} \cos (x) - 8 x \sin (x) - 8 \cos (x)$ with respect to $x$ is $\frac{d}{d x} [x^{3} \cos (x)] + \frac{d}{d x} [- 8 x \sin (x)] + \frac{d}{d x} [- 8 \cos (x)]$ .

$\frac{d}{d x} [x^{3} \cos (x)] + \frac{d}{d x} [- 8 x \sin (x)] + \frac{d}{d x} [- 8 \cos (x)]$

Step 2

Evaluate $\frac{d}{d x} [x^{3} \cos (x)]$ .

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Step 2.1

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 $f (x) = x^{3}$ and $g (x) = \cos (x)$ .

$x^{3} \frac{d}{d x} [\cos (x)] + \cos (x) \frac{d}{d x} [x^{3}] + \frac{d}{d x} [- 8 x \sin (x)] + \frac{d}{d x} [- 8 \cos (x)]$

Step 2.2

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

$x^{3} (- \sin (x)) + \cos (x) \frac{d}{d x} [x^{3}] + \frac{d}{d x} [- 8 x \sin (x)] + \frac{d}{d x} [- 8 \cos (x)]$

Step 2.3

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

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) + \frac{d}{d x} [- 8 x \sin (x)] + \frac{d}{d x} [- 8 \cos (x)]$

Step 3

Evaluate $\frac{d}{d x} [- 8 x \sin (x)]$ .

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Step 3.1

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

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 \frac{d}{d x} [x \sin (x)] + \frac{d}{d x} [- 8 \cos (x)]$

Step 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 $g (x) = \sin (x)$ .

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 (x \frac{d}{d x} [\sin (x)] + \sin (x) \frac{d}{d x} [x]) + \frac{d}{d x} [- 8 \cos (x)]$

Step 3.3

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

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 (x \cos (x) + \sin (x) \frac{d}{d x} [x]) + \frac{d}{d x} [- 8 \cos (x)]$

Step 3.4

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

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 (x \cos (x) + \sin (x) \cdot 1) + \frac{d}{d x} [- 8 \cos (x)]$

Step 3.5

Multiply $\sin (x)$ by $1$ .

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 (x \cos (x) + \sin (x)) + \frac{d}{d x} [- 8 \cos (x)]$

Step 4

Evaluate $\frac{d}{d x} [- 8 \cos (x)]$ .

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Step 4.1

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

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 (x \cos (x) + \sin (x)) - 8 \frac{d}{d x} [\cos (x)]$

Step 4.2

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

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 (x \cos (x) + \sin (x)) - 8 (- \sin (x))$

Step 4.3

Multiply $- 1$ by $- 8$ .

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 (x \cos (x) + \sin (x)) + 8 \sin (x)$

Step 5

Simplify.

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Step 5.1

Apply the distributive property.

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 (x \cos (x)) - 8 \sin (x) + 8 \sin (x)$

Step 5.2

Combine terms.

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Step 5.2.1

Add $- 8 \sin (x)$ and $8 \sin (x)$ .

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 x \cos (x) + 0$

Step 5.2.2

Add $x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 x \cos (x)$ and $0$ .

$x^{3} (- \sin (x)) + \cos (x) (3 x^{2}) - 8 x \cos (x)$

Step 5.3

Reorder terms.

$- x^{3} \sin (x) + 3 x^{2} \cos (x) - 8 x \cos (x)$