Trigonometry Examples

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

Step 1

Start on the left side.

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

Step 2

Simplify the expression.

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Step 2.1

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

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

Step 2.2

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

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

Step 2.3

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

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Step 2.3.1

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

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

Step 2.3.2

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

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

Step 2.3.3

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

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

Step 2.4

Combine the numerators over the common denominator.

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

Step 2.5

Simplify the numerator.

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Step 2.5.1

Multiply $- \cos (x) \cos (x)$ .

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Step 2.5.1.1

Raise $\cos (x)$ to the power of $1$ .

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

Step 2.5.1.2

Raise $\cos (x)$ to the power of $1$ .

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

Step 2.5.1.3

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

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

Step 2.5.1.4

Add $1$ and $1$ .

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

Step 2.5.2

Move $- \cos^{2} (x)$ .

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

Step 2.5.3

Apply pythagorean identity.

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

Step 2.5.4

Factor $\sin (x)$ out of $\sin^{2} (x) + \sin (x)$ .

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Step 2.5.4.1

Factor $\sin (x)$ out of $\sin^{2} (x)$ .

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

Step 2.5.4.2

Multiply by $1$ .

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

Step 2.5.4.3

Factor $\sin (x)$ out of $\sin (x) \sin (x) + \sin (x) \cdot 1$ .

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

Step 2.6

Cancel the common factor of $\sin (x) + 1$ and $1 + \sin (x)$ .

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Step 2.6.1

Reorder terms.

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

Step 2.6.2

Cancel the common factor.

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

Step 2.6.3

Rewrite the expression.

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

Step 3

Rewrite $\frac{\sin (x)}{\cos (x)}$ as $\tan (x)$ .

$\tan (x)$

Step 4

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

$\frac{1}{\cos (x)} - \frac{\cos (x)}{1 + \sin (x)} = \tan (x)$ is an identity