Precalculus Examples

$\cos (x) (1 + \tan^{2} (x)) = \sec (x)$

Step 1

Start on the left side.

$\cos (x) (1 + \tan^{2} (x))$

Step 2

Apply Pythagorean identity.

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Step 2.1

Rearrange terms.

$\cos (x) (\tan^{2} (x) + 1)$

Step 2.2

Apply pythagorean identity.

$\cos (x) \sec^{2} (x)$

Step 3

Convert to sines and cosines.

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Step 3.1

Apply the reciprocal identity to $\sec (x)$ .

$\cos (x) {(\frac{1}{\cos (x)})}^{2}$

Step 3.2

Apply the product rule to $\frac{1}{\cos (x)}$ .

$\cos (x) \frac{1^{2}}{\cos^{2} (x)}$

Step 4

Simplify.

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Step 4.1

One to any power is one.

$\cos (x) \frac{1}{{\cos (x)}^{2}}$

Step 4.2

Cancel the common factor of $\cos (x)$ .

$\frac{1}{\cos (x)}$

Step 5

Rewrite $\frac{1}{\cos (x)}$ as $\sec (x)$ .

$\sec (x)$

Step 6

Because the two sides have been shown to be equivalent, the equation is an identity.

$\cos (x) (1 + \tan^{2} (x)) = \sec (x)$ is an identity