Calculus Examples

$\int \sec^{4} (x) d x$

Step 1

Simplify the expression.

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Step 1.1

Rewrite $4$ as $2$ plus $2$

$\int {\sec (x)}^{2 + 2} d x$

Step 1.2

Rewrite ${\sec (x)}^{2 + 2}$ as $\sec^{2} (x) \sec^{2} (x)$ .

$\int \sec^{2} (x) \sec^{2} (x) d x$

Step 2

Using the Pythagorean Identity, rewrite $\sec^{2} (x)$ as $1 + \tan^{2} (x)$ .

$\int (1 + \tan^{2} (x)) \sec^{2} (x) d x$

Step 3

Let $u = \tan (x)$ . Then $d u = \sec^{2} (x) d x$ , so $\frac{1}{\sec^{2} (x)} d u = d x$ . Rewrite using $u$ and $d$ $u$ .

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Step 3.1

Let $u = \tan (x)$ . Find $\frac{d u}{d x}$ .

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Step 3.1.1

Differentiate $\tan (x)$ .

$\frac{d}{d x} [\tan (x)]$

Step 3.1.2

The derivative of $\tan (x)$ with respect to $x$ is $\sec^{2} (x)$ .

$\sec^{2} (x)$

Step 3.2

Rewrite the problem using $u$ and $d u$ .

$\int 1 + u^{2} d u$

Step 4

Split the single integral into multiple integrals.

$\int d u + \int u^{2} d u$

Step 5

Apply the constant rule.

$u + C + \int u^{2} d u$

Step 6

By the Power Rule, the integral of $u^{2}$ with respect to $u$ is $\frac{1}{3} u^{3}$ .

$u + C + \frac{1}{3} u^{3} + C$

Step 7

Simplify.

$u + \frac{1}{3} u^{3} + C$

Step 8

Replace all occurrences of $u$ with $\tan (x)$ .

$\tan (x) + \frac{1}{3} \tan^{3} (x) + C$