Precalculus Examples

$2 \sec^{2} (x) = \frac{1}{1 + \sin (x)} + \frac{1}{1 - \sin (x)}$

Step 1

Start on the right side.

$\frac{1}{1 + \sin (x)} + \frac{1}{1 - \sin (x)}$

Step 2

Add fractions.

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Step 2.1

To write $\frac{1}{1 + \sin (x)}$ as a fraction with a common denominator, multiply by $\frac{1 - \sin (x)}{1 - \sin (x)}$ .

$\frac{1}{1 + \sin (x)} \cdot \frac{1 - \sin (x)}{1 - \sin (x)} + \frac{1}{1 - \sin (x)}$

Step 2.2

To write $\frac{1}{1 - \sin (x)}$ as a fraction with a common denominator, multiply by $\frac{1 + \sin (x)}{1 + \sin (x)}$ .

$\frac{1}{1 + \sin (x)} \cdot \frac{1 - \sin (x)}{1 - \sin (x)} + \frac{1}{1 - \sin (x)} \cdot \frac{1 + \sin (x)}{1 + \sin (x)}$

Step 2.3

Write each expression with a common denominator of $(1 + \sin (x)) (1 - \sin (x))$ , by multiplying each by an appropriate factor of $1$ .

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Step 2.3.1

Multiply $\frac{1}{1 + \sin (x)}$ by $\frac{1 - \sin (x)}{1 - \sin (x)}$ .

$\frac{1 - \sin (x)}{(1 + \sin (x)) (1 - \sin (x))} + \frac{1}{1 - \sin (x)} \cdot \frac{1 + \sin (x)}{1 + \sin (x)}$

Step 2.3.2

Multiply $\frac{1}{1 - \sin (x)}$ by $\frac{1 + \sin (x)}{1 + \sin (x)}$ .

$\frac{1 - \sin (x)}{(1 + \sin (x)) (1 - \sin (x))} + \frac{1 + \sin (x)}{(1 - \sin (x)) (1 + \sin (x))}$

Step 2.3.3

Reorder the factors of $(1 - \sin (x)) (1 + \sin (x))$ .

$\frac{1 - \sin (x)}{(1 + \sin (x)) (1 - \sin (x))} + \frac{1 + \sin (x)}{(1 + \sin (x)) (1 - \sin (x))}$

Step 2.4

Combine the numerators over the common denominator.

$\frac{1 - \sin (x) + 1 + \sin (x)}{(1 + \sin (x)) (1 - \sin (x))}$

Step 3

Simplify numerator.

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Step 3.1

Add $1$ and $1$ .

$\frac{2 - \sin (x) + \sin (x)}{(1 + \sin (x)) (1 - \sin (x))}$

Step 3.2

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

$\frac{2 + 0}{(1 + \sin (x)) (1 - \sin (x))}$

Step 3.3

Add $2$ and $0$ .

$\frac{2}{(1 + \sin (x)) (1 - \sin (x))}$

Step 4

Simplify denominator.

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Step 4.1

Expand $(1 + \sin (x)) (1 - \sin (x))$ using the FOIL Method.

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Step 4.1.1

Apply the distributive property.

$\frac{2}{1 (1 - \sin (x)) + \sin (x) (1 - \sin (x))}$

Step 4.1.2

Apply the distributive property.

$\frac{2}{1 \cdot 1 + 1 (- \sin (x)) + \sin (x) (1 - \sin (x))}$

Step 4.1.3

Apply the distributive property.

$\frac{2}{1 \cdot 1 + 1 (- \sin (x)) + \sin (x) \cdot 1 + \sin (x) (- \sin (x))}$

Step 4.2

Simplify and combine like terms.

$\frac{2}{1 - \sin^{2} (x)}$

Step 5

Apply pythagorean identity.

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

Step 6

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

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

Step 7

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

$2 \sec^{2} (x) = \frac{1}{1 + \sin (x)} + \frac{1}{1 - \sin (x)}$ is an identity