Calculus Examples

$y = x^{2} - x \cos (x)$

Step 1

Differentiate both sides of the equation.

$\frac{d}{d x} (y) = \frac{d}{d x} (x^{2} - x \cos (x))$

Step 2

The derivative of $y$ with respect to $x$ is $y'$ .

$y'$

Step 3

Differentiate the right side of the equation.

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Step 3.1

Differentiate.

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Step 3.1.1

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

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

Step 3.1.2

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

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

Step 3.2

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

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Step 3.2.1

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

$2 x - \frac{d}{d x} [x \cos (x)]$

Step 3.2.2

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 $g (x) = \cos (x)$ .

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

Step 3.2.3

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

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

Step 3.2.4

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

$2 x - (x (- \sin (x)) + \cos (x) \cdot 1)$

Step 3.2.5

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

$2 x - (x (- \sin (x)) + \cos (x))$

Step 3.3

Simplify.

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Step 3.3.1

Apply the distributive property.

$2 x - (x (- \sin (x))) - \cos (x)$

Step 3.3.2

Combine terms.

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Step 3.3.2.1

Multiply $- 1$ by $- 1$ .

$2 x + 1 (x (\sin (x))) - \cos (x)$

Step 3.3.2.2

Multiply $x$ by $1$ .

$2 x + x \sin (x) - \cos (x)$

Step 3.3.3

Reorder terms.

$x \sin (x) + 2 x - \cos (x)$

Step 4

Reform the equation by setting the left side equal to the right side.

$y' = x \sin (x) + 2 x - \cos (x)$

Step 5

Replace $y'$ with $\frac{d y}{d x}$ .

$\frac{d y}{d x} = x \sin (x) + 2 x - \cos (x)$