Trigonometry Examples

$\tan (- \frac{π}{8})$

Step 1

Add full rotations of $2 π$ until the angle is greater than or equal to $0$ and less than $2 π$ .

$\tan (\frac{15 π}{8})$

Step 2

The exact value of $\tan (\frac{15 π}{8})$ is $- \sqrt{3 - 2 \sqrt{2}}$ .

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Step 2.1

Rewrite $\frac{15 π}{8}$ as an angle where the values of the six trigonometric functions are known divided by $2$ .

$\tan (\frac{\frac{15 π}{4}}{2})$

Step 2.2

Apply the tangent half-angle identity.

$\pm \sqrt{\frac{1 - \cos (\frac{15 π}{4})}{1 + \cos (\frac{15 π}{4})}}$

Step 2.3

Change the $\pm$ to $-$ because tangent is negative in the fourth quadrant.

$- \sqrt{\frac{1 - \cos (\frac{15 π}{4})}{1 + \cos (\frac{15 π}{4})}}$

Step 2.4

Simplify $- \sqrt{\frac{1 - \cos (\frac{15 π}{4})}{1 + \cos (\frac{15 π}{4})}}$ .

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Step 2.4.1

Subtract full rotations of $2 π$ until the angle is greater than or equal to $0$ and less than $2 π$ .

$- \sqrt{\frac{1 - \cos (\frac{7 π}{4})}{1 + \cos (\frac{15 π}{4})}}$

Step 2.4.2

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.

$- \sqrt{\frac{1 - \cos (\frac{π}{4})}{1 + \cos (\frac{15 π}{4})}}$

Step 2.4.3

The exact value of $\cos (\frac{π}{4})$ is $\frac{\sqrt{2}}{2}$ .

$- \sqrt{\frac{1 - \frac{\sqrt{2}}{2}}{1 + \cos (\frac{15 π}{4})}}$

Step 2.4.4

Write $1$ as a fraction with a common denominator.

$- \sqrt{\frac{\frac{2}{2} - \frac{\sqrt{2}}{2}}{1 + \cos (\frac{15 π}{4})}}$

Step 2.4.5

Combine the numerators over the common denominator.

$- \sqrt{\frac{\frac{2 - \sqrt{2}}{2}}{1 + \cos (\frac{15 π}{4})}}$

Step 2.4.6

Subtract full rotations of $2 π$ until the angle is greater than or equal to $0$ and less than $2 π$ .

$- \sqrt{\frac{\frac{2 - \sqrt{2}}{2}}{1 + \cos (\frac{7 π}{4})}}$

Step 2.4.7

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.

$- \sqrt{\frac{\frac{2 - \sqrt{2}}{2}}{1 + \cos (\frac{π}{4})}}$

Step 2.4.8

The exact value of $\cos (\frac{π}{4})$ is $\frac{\sqrt{2}}{2}$ .

$- \sqrt{\frac{\frac{2 - \sqrt{2}}{2}}{1 + \frac{\sqrt{2}}{2}}}$

Step 2.4.9

Write $1$ as a fraction with a common denominator.

$- \sqrt{\frac{\frac{2 - \sqrt{2}}{2}}{\frac{2}{2} + \frac{\sqrt{2}}{2}}}$

Step 2.4.10

Combine the numerators over the common denominator.

$- \sqrt{\frac{\frac{2 - \sqrt{2}}{2}}{\frac{2 + \sqrt{2}}{2}}}$

Step 2.4.11

Multiply the numerator by the reciprocal of the denominator.

$- \sqrt{\frac{2 - \sqrt{2}}{2} \cdot \frac{2}{2 + \sqrt{2}}}$

Step 2.4.12

Cancel the common factor of $2$ .

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Step 2.4.12.1

Cancel the common factor.

$- \sqrt{\frac{2 - \sqrt{2}}{2} \cdot \frac{2}{2 + \sqrt{2}}}$

Step 2.4.12.2

Rewrite the expression.

$- \sqrt{(2 - \sqrt{2}) \frac{1}{2 + \sqrt{2}}}$

Step 2.4.13

Multiply $\frac{1}{2 + \sqrt{2}}$ by $\frac{2 - \sqrt{2}}{2 - \sqrt{2}}$ .

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

Step 2.4.14

Multiply $\frac{1}{2 + \sqrt{2}}$ by $\frac{2 - \sqrt{2}}{2 - \sqrt{2}}$ .

$- \sqrt{(2 - \sqrt{2}) \frac{2 - \sqrt{2}}{(2 + \sqrt{2}) (2 - \sqrt{2})}}$

Step 2.4.15

Expand the denominator using the FOIL method.

$- \sqrt{(2 - \sqrt{2}) \frac{2 - \sqrt{2}}{4 - 2 \sqrt{2} + \sqrt{2} \cdot 2 - {\sqrt{2}}^{2}}}$

Step 2.4.16

Simplify.

$- \sqrt{(2 - \sqrt{2}) \frac{2 - \sqrt{2}}{2}}$

Step 2.4.17

Apply the distributive property.

$- \sqrt{2 \frac{2 - \sqrt{2}}{2} - \sqrt{2} \frac{2 - \sqrt{2}}{2}}$

Step 2.4.18

Cancel the common factor of $2$ .

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Step 2.4.18.1

Cancel the common factor.

$- \sqrt{2 \frac{2 - \sqrt{2}}{2} - \sqrt{2} \frac{2 - \sqrt{2}}{2}}$

Step 2.4.18.2

Rewrite the expression.

$- \sqrt{2 - \sqrt{2} - \sqrt{2} \frac{2 - \sqrt{2}}{2}}$

Step 2.4.19

Combine $\frac{2 - \sqrt{2}}{2}$ and $\sqrt{2}$ .

$- \sqrt{2 - \sqrt{2} - \frac{(2 - \sqrt{2}) \sqrt{2}}{2}}$

Step 2.4.20

Simplify each term.

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Step 2.4.20.1

Apply the distributive property.

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - \sqrt{2} \sqrt{2}}{2}}$

Step 2.4.20.2

Multiply $- \sqrt{2} \sqrt{2}$ .

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Step 2.4.20.2.1

Raise $\sqrt{2}$ to the power of $1$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - ({\sqrt{2}}^{1} \sqrt{2})}{2}}$

Step 2.4.20.2.2

Raise $\sqrt{2}$ to the power of $1$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - ({\sqrt{2}}^{1} {\sqrt{2}}^{1})}{2}}$

Step 2.4.20.2.3

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

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - {\sqrt{2}}^{1 + 1}}{2}}$

Step 2.4.20.2.4

Add $1$ and $1$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - {\sqrt{2}}^{2}}{2}}$

Step 2.4.20.3

Simplify each term.

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Step 2.4.20.3.1

Rewrite ${\sqrt{2}}^{2}$ as $2$ .

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Step 2.4.20.3.1.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{2}$ as $2^{\frac{1}{2}}$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - {(2^{\frac{1}{2}})}^{2}}{2}}$

Step 2.4.20.3.1.2

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - 2^{\frac{1}{2} \cdot 2}}{2}}$

Step 2.4.20.3.1.3

Combine $\frac{1}{2}$ and $2$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - 2^{\frac{2}{2}}}{2}}$

Step 2.4.20.3.1.4

Cancel the common factor of $2$ .

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Step 2.4.20.3.1.4.1

Cancel the common factor.

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - 2^{\frac{2}{2}}}{2}}$

Step 2.4.20.3.1.4.2

Rewrite the expression.

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - 2^{1}}{2}}$

Step 2.4.20.3.1.5

Evaluate the exponent.

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - 1 \cdot 2}{2}}$

Step 2.4.20.3.2

Multiply $- 1$ by $2$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 \sqrt{2} - 2}{2}}$

Step 2.4.20.4

Cancel the common factor of $2 \sqrt{2} - 2$ and $2$ .

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Step 2.4.20.4.1

Factor $2$ out of $2 \sqrt{2}$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 (\sqrt{2}) - 2}{2}}$

Step 2.4.20.4.2

Factor $2$ out of $- 2$ .

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

Step 2.4.20.4.3

Factor $2$ out of $2 (\sqrt{2}) + 2 (- 1)$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 (\sqrt{2} - 1)}{2}}$

Step 2.4.20.4.4

Cancel the common factors.

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Step 2.4.20.4.4.1

Factor $2$ out of $2$ .

$- \sqrt{2 - \sqrt{2} - \frac{2 (\sqrt{2} - 1)}{2 (1)}}$

Step 2.4.20.4.4.2

Cancel the common factor.

$- \sqrt{2 - \sqrt{2} - \frac{2 (\sqrt{2} - 1)}{2 \cdot 1}}$

Step 2.4.20.4.4.3

Rewrite the expression.

$- \sqrt{2 - \sqrt{2} - \frac{\sqrt{2} - 1}{1}}$

Step 2.4.20.4.4.4

Divide $\sqrt{2} - 1$ by $1$ .

$- \sqrt{2 - \sqrt{2} - (\sqrt{2} - 1)}$

Step 2.4.20.5

Apply the distributive property.

$- \sqrt{2 - \sqrt{2} - \sqrt{2} - - 1}$

Step 2.4.20.6

Multiply $- 1$ by $- 1$ .

$- \sqrt{2 - \sqrt{2} - \sqrt{2} + 1}$

Step 2.4.21

Add $2$ and $1$ .

$- \sqrt{3 - \sqrt{2} - \sqrt{2}}$

Step 2.4.22

Subtract $\sqrt{2}$ from $- \sqrt{2}$ .

$- \sqrt{3 - 2 \sqrt{2}}$

Step 3

The result can be shown in multiple forms.

Exact Form:

$- \sqrt{3 - 2 \sqrt{2}}$

Decimal Form:

$- 0.41421356 \dots$