Trigonometry Examples

$\frac{\tan (a) - \tan (b)}{\cot (b) - \cot (a)} = \frac{\tan (b)}{\cot (a)}$

Step 1

Start on the left side.

$\frac{\tan (a) - \tan (b)}{\cot (b) - \cot (a)}$

Step 2

Convert to sines and cosines.

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Step 2.1

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

$\frac{\frac{\sin (a)}{\cos (a)} - \tan (b)}{\cot (b) - \cot (a)}$

Step 2.2

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

$\frac{\frac{\sin (a)}{\cos (a)} - \frac{\sin (b)}{\cos (b)}}{\cot (b) - \cot (a)}$

Step 2.3

Write $\cot (b)$ in sines and cosines using the quotient identity.

$\frac{\frac{\sin (a)}{\cos (a)} - \frac{\sin (b)}{\cos (b)}}{\frac{\cos (b)}{\sin (b)} - \cot (a)}$

Step 2.4

Write $\cot (a)$ in sines and cosines using the quotient identity.

$\frac{\frac{\sin (a)}{\cos (a)} - \frac{\sin (b)}{\cos (b)}}{\frac{\cos (b)}{\sin (b)} - \frac{\cos (a)}{\sin (a)}}$

Step 3

Simplify.

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Step 3.1

Multiply the numerator and denominator of the fraction by $\cos (a) \cos (b) \sin (b) \sin (a)$ .

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Step 3.1.1

Multiply $\frac{\frac{\sin (a)}{\cos (a)} - \frac{\sin (b)}{\cos (b)}}{\frac{\cos (b)}{\sin (b)} - \frac{\cos (a)}{\sin (a)}}$ by $\frac{\cos (a) \cos (b) \sin (b) \sin (a)}{\cos (a) \cos (b) \sin (b) \sin (a)}$ .

$\frac{\cos (a) \cos (b) \sin (b) \sin (a)}{\cos (a) \cos (b) \sin (b) \sin (a)} \cdot \frac{\frac{\sin (a)}{\cos (a)} - \frac{\sin (b)}{\cos (b)}}{\frac{\cos (b)}{\sin (b)} - \frac{\cos (a)}{\sin (a)}}$

Step 3.1.2

Combine.

$\frac{\cos (a) \cos (b) \sin (b) \sin (a) (\frac{\sin (a)}{\cos (a)} - \frac{\sin (b)}{\cos (b)})}{\cos (a) \cos (b) \sin (b) \sin (a) (\frac{\cos (b)}{\sin (b)} - \frac{\cos (a)}{\sin (a)})}$

Step 3.2

Apply the distributive property.

$\frac{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\sin (a)}{\cos (a)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\sin (b)}{\cos (b)})}{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3

Simplify by cancelling.

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Step 3.3.1

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

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Step 3.3.1.1

Factor $\cos (a)$ out of $\cos (a) \cos (b) \sin (b) \sin (a)$ .

$\frac{\cos (a) (\cos (b) \sin (b) \sin (a)) \frac{\sin (a)}{\cos (a)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\sin (b)}{\cos (b)})}{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.1.2

Cancel the common factor.

Step 3.3.1.3

Rewrite the expression.

$\frac{\cos (b) \sin (b) \sin (a) \sin (a) + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\sin (b)}{\cos (b)})}{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.2

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

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

Step 3.3.3

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

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

Step 3.3.4

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

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

Step 3.3.5

Add $1$ and $1$ .

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\sin (b)}{\cos (b)})}{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.6

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

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Step 3.3.6.1

Move the leading negative in $- \frac{\sin (b)}{\cos (b)}$ into the numerator.

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \cos (b) \sin (b) \sin (a) \frac{- \sin (b)}{\cos (b)}}{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.6.2

Factor $\cos (b)$ out of $\cos (a) \cos (b) \sin (b) \sin (a)$ .

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (b) (\cos (a) \sin (b) \sin (a)) \frac{- \sin (b)}{\cos (b)}}{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.6.3

Cancel the common factor.

Step 3.3.6.4

Rewrite the expression.

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (b) \sin (a) (- \sin (b))}{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.7

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

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

Step 3.3.8

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

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

Step 3.3.9

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

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

Step 3.3.10

Add $1$ and $1$ .

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) \cos (b) \sin (b) \sin (a) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.11

Cancel the common factor of $\sin (b)$ .

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Step 3.3.11.1

Factor $\sin (b)$ out of $\cos (a) \cos (b) \sin (b) \sin (a)$ .

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\sin (b) (\cos (a) \cos (b) \sin (a)) \frac{\cos (b)}{\sin (b)} + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.11.2

Cancel the common factor.

Step 3.3.11.3

Rewrite the expression.

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) \cos (b) \sin (a) \cos (b) + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.12

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

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

Step 3.3.13

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

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

Step 3.3.14

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

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

Step 3.3.15

Add $1$ and $1$ .

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) {\cos (b)}^{2} \sin (a) + \cos (a) \cos (b) \sin (b) \sin (a) (- \frac{\cos (a)}{\sin (a)})}$

Step 3.3.16

Cancel the common factor of $\sin (a)$ .

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Step 3.3.16.1

Move the leading negative in $- \frac{\cos (a)}{\sin (a)}$ into the numerator.

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) {\cos (b)}^{2} \sin (a) + \cos (a) \cos (b) \sin (b) \sin (a) \frac{- \cos (a)}{\sin (a)}}$

Step 3.3.16.2

Factor $\sin (a)$ out of $\cos (a) \cos (b) \sin (b) \sin (a)$ .

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) {\cos (b)}^{2} \sin (a) + \sin (a) (\cos (a) \cos (b) \sin (b)) \frac{- \cos (a)}{\sin (a)}}$

Step 3.3.16.3

Cancel the common factor.

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) {\cos (b)}^{2} \sin (a) + \sin (a) (\cos (a) \cos (b) \sin (b)) \frac{- \cos (a)}{\sin (a)}}$

Step 3.3.16.4

Rewrite the expression.

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) {\cos (b)}^{2} \sin (a) + \cos (a) \cos (b) \sin (b) (- \cos (a))}$

Step 3.3.17

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

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

Step 3.3.18

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

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

Step 3.3.19

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

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

Step 3.3.20

Add $1$ and $1$ .

$\frac{\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) {\cos (b)}^{2} \sin (a) + \cos (b) \sin (b) (- {\cos (a)}^{2})}$

Step 3.4

Factor $\sin (b) \sin (a)$ out of $\cos (b) \sin (b) {\sin (a)}^{2} + \cos (a) \sin (a) (- {\sin (b)}^{2})$ .

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Step 3.4.1

Factor $\sin (b) \sin (a)$ out of $\cos (b) \sin (b) {\sin (a)}^{2}$ .

$\frac{\sin (b) \sin (a) (\cos (b) \sin (a)) + \cos (a) \sin (a) (- {\sin (b)}^{2})}{\cos (a) {\cos (b)}^{2} \sin (a) + \cos (b) \sin (b) (- {\cos (a)}^{2})}$

Step 3.4.2

Factor $\sin (b) \sin (a)$ out of $\cos (a) \sin (a) (- {\sin (b)}^{2})$ .

$\frac{\sin (b) \sin (a) (\cos (b) \sin (a)) + \sin (b) \sin (a) (\cos (a) (- \sin (b)))}{\cos (a) {\cos (b)}^{2} \sin (a) + \cos (b) \sin (b) (- {\cos (a)}^{2})}$

Step 3.4.3

Factor $\sin (b) \sin (a)$ out of $\sin (b) \sin (a) (\cos (b) \sin (a)) + \sin (b) \sin (a) (\cos (a) (- \sin (b)))$ .

$\frac{\sin (b) \sin (a) (\cos (b) \sin (a) + \cos (a) (- \sin (b)))}{\cos (a) {\cos (b)}^{2} \sin (a) + \cos (b) \sin (b) (- {\cos (a)}^{2})}$

Step 3.5

Factor $\cos (a) \cos (b)$ out of $\cos (a) {\cos (b)}^{2} \sin (a) + \cos (b) \sin (b) (- {\cos (a)}^{2})$ .

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Step 3.5.1

Factor $\cos (a) \cos (b)$ out of $\cos (a) {\cos (b)}^{2} \sin (a)$ .

$\frac{\sin (b) \sin (a) (\cos (b) \sin (a) + \cos (a) (- \sin (b)))}{\cos (a) \cos (b) (\cos (b) \sin (a)) + \cos (b) \sin (b) (- {\cos (a)}^{2})}$

Step 3.5.2

Factor $\cos (a) \cos (b)$ out of $\cos (b) \sin (b) (- {\cos (a)}^{2})$ .

$\frac{\sin (b) \sin (a) (\cos (b) \sin (a) + \cos (a) (- \sin (b)))}{\cos (a) \cos (b) (\cos (b) \sin (a)) + \cos (a) \cos (b) (\sin (b) (- \cos (a)))}$

Step 3.5.3

Factor $\cos (a) \cos (b)$ out of $\cos (a) \cos (b) (\cos (b) \sin (a)) + \cos (a) \cos (b) (\sin (b) (- \cos (a)))$ .

$\frac{\sin (b) \sin (a) (\cos (b) \sin (a) + \cos (a) (- \sin (b)))}{\cos (a) \cos (b) (\cos (b) \sin (a) + \sin (b) (- \cos (a)))}$

Step 3.6

Reorder the terms.

$\frac{\sin (b) \sin (a) (\cos (b) \sin (a) - 1 \cdot \cos (a) \sin (b))}{\cos (a) \cos (b) (\cos (b) \sin (a) - 1 \cdot \sin (b) \cos (a))}$

Step 3.7

Cancel the common factor of $\cos (b) \sin (a) - 1 \cdot \cos (a) \sin (b)$ and $\cos (b) \sin (a) - 1 \cdot \sin (b) \cos (a)$ .

$\frac{\sin (b) \sin (a)}{\cos (a) \cos (b)}$

Step 4

Reorder terms.

$\frac{\sin (a) \sin (b)}{\cos (a) \cos (b)}$

Step 5

Rewrite $\frac{\sin (a) \sin (b)}{\cos (a) \cos (b)}$ as $\frac{\tan (b)}{\cot (a)}$ .

$\frac{\tan (b)}{\cot (a)}$

Step 6

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

$\frac{\tan (a) - \tan (b)}{\cot (b) - \cot (a)} = \frac{\tan (b)}{\cot (a)}$ is an identity