Precalculus Examples

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

Step 1

Start on the left side.

$\frac{1}{\sec (x) + \tan (x)}$

Step 2

Convert to sines and cosines.

Tap for more steps...

Step 2.1

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

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

Step 2.2

Write $\tan (x)$ in sines and cosines using the quotient identity.

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

Step 3

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

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

Step 4

Combine.

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

Step 5

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

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

Step 6

Simplify denominator.

Tap for more steps...

Step 6.1

Expand $(\frac{1}{\cos (x)} + \frac{\sin (x)}{\cos (x)}) (\frac{1}{\cos (x)} + \frac{\sin (x)}{\cos (x)})$ using the FOIL Method.

Tap for more steps...

Step 6.1.1

Apply the distributive property.

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

Step 6.1.2

Apply the distributive property.

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

Step 6.1.3

Apply the distributive property.

Step 6.2

Simplify and combine like terms.

Tap for more steps...

Step 6.2.1

Simplify each term.

Tap for more steps...

Step 6.2.1.1

Multiply $\frac{1}{\cos (x)} \cdot \frac{1}{\cos (x)}$ .

Tap for more steps...

Step 6.2.1.1.1

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

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

Step 6.2.1.1.2

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

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

Step 6.2.1.1.3

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

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

Step 6.2.1.1.4

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

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

Step 6.2.1.1.5

Add $1$ and $1$ .

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

Step 6.2.1.2

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

Tap for more steps...

Step 6.2.1.2.1

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

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

Step 6.2.1.2.2

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

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

Step 6.2.1.2.3

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

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

Step 6.2.1.2.4

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

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

Step 6.2.1.2.5

Add $1$ and $1$ .

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

Step 6.2.1.3

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

Tap for more steps...

Step 6.2.1.3.1

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

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

Step 6.2.1.3.2

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

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

Step 6.2.1.3.3

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

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

Step 6.2.1.3.4

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

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

Step 6.2.1.3.5

Add $1$ and $1$ .

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

Step 6.2.1.4

Multiply $\frac{\sin (x)}{\cos (x)} \cdot \frac{\sin (x)}{\cos (x)}$ .

Tap for more steps...

Step 6.2.1.4.1

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

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

Step 6.2.1.4.2

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

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

Step 6.2.1.4.3

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

Step 6.2.1.4.4

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

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

Step 6.2.1.4.5

Add $1$ and $1$ .

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

Step 6.2.1.4.6

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

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

Step 6.2.1.4.7

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

Step 6.2.1.4.8

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

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

Step 6.2.1.4.9

Add $1$ and $1$ .

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

Step 6.2.2

Combine the numerators over the common denominator.

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

Step 6.3

Combine the numerators over the common denominator.

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

Step 6.4

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

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

Step 6.5

Factor using the perfect square rule.

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

Step 7

Apply Pythagorean identity in reverse.

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

Step 8

Simplify.

Tap for more steps...

Step 8.1

Multiply the numerator by the reciprocal of the denominator.

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

Step 8.2

Simplify the numerator.

Tap for more steps...

Step 8.2.1

Rewrite $1$ as $1^{2}$ .

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

Step 8.2.2

Since both terms are perfect squares, factor using the difference of squares formula, $a^{2} - b^{2} = (a + b) (a - b)$ where $a = 1$ and $b = \sin (x)$ .

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

Step 8.3

Cancel the common factors.

Tap for more steps...

Step 8.3.1

Factor $1 + \sin (x)$ out of ${(1 + \sin (x))}^{2}$ .

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

Step 8.3.2

Cancel the common factor.

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

Step 8.3.3

Rewrite the expression.

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

Step 8.4

Apply the distributive property.

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

Step 8.5

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

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

Step 8.6

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

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

Step 8.7

Combine the numerators over the common denominator.

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

Step 8.8

Simplify each term.

Tap for more steps...

Step 8.8.1

Apply the distributive property.

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

Step 8.8.2

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

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

Step 8.8.3

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

Tap for more steps...

Step 8.8.3.1

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

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

Step 8.8.3.2

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

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

Step 8.8.3.3

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

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

Step 8.8.3.4

Add $1$ and $1$ .

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

Step 8.9

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

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

Step 8.10

Add $1$ and $0$ .

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

Step 8.11

Simplify the numerator.

Tap for more steps...

Step 8.11.1

Rewrite $1$ as $1^{2}$ .

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

Step 8.11.2

Since both terms are perfect squares, factor using the difference of squares formula, $a^{2} - b^{2} = (a + b) (a - b)$ where $a = 1$ and $b = \sin (x)$ .

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

Step 8.12

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

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

Step 9

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

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