Trigonometry Examples

$\arctan (\tan (\frac{7 π}{8}))$

Step 1

Rewrite $\frac{7 π}{8}$ as an angle where the values of the six trigonometric functions are known divided by $2$ .

$\arctan (\tan (\frac{\frac{7 π}{4}}{2}))$

Step 2

Apply the tangent half-angle identity.

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

Step 3

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

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

Step 4

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

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Step 4.1

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

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

Step 4.2

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

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

Step 4.3

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

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

Step 4.4

Combine the numerators over the common denominator.

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

Step 4.5

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

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

Step 4.6

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

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

Step 4.7

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

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

Step 4.8

Combine the numerators over the common denominator.

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

Step 4.9

Multiply the numerator by the reciprocal of the denominator.

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

Step 4.10

Cancel the common factor of $2$ .

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Step 4.10.1

Cancel the common factor.

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

Step 4.10.2

Rewrite the expression.

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

Step 4.11

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

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

Step 4.12

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

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

Step 4.13

Expand the denominator using the FOIL method.

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

Step 4.14

Simplify.

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

Step 4.15

Apply the distributive property.

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

Step 4.16

Cancel the common factor of $2$ .

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Step 4.16.1

Cancel the common factor.

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

Step 4.16.2

Rewrite the expression.

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

Step 4.17

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

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

Step 4.18

Simplify each term.

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Step 4.18.1

Apply the distributive property.

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

Step 4.18.2

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

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Step 4.18.2.1

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

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

Step 4.18.2.2

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

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

Step 4.18.2.3

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

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

Step 4.18.2.4

Add $1$ and $1$ .

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

Step 4.18.3

Simplify each term.

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Step 4.18.3.1

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

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Step 4.18.3.1.1

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

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

Step 4.18.3.1.2

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

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

Step 4.18.3.1.3

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

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

Step 4.18.3.1.4

Cancel the common factor of $2$ .

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Step 4.18.3.1.4.1

Cancel the common factor.

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

Step 4.18.3.1.4.2

Rewrite the expression.

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

Step 4.18.3.1.5

Evaluate the exponent.

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

Step 4.18.3.2

Multiply $- 1$ by $2$ .

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

Step 4.18.4

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

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Step 4.18.4.1

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

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

Step 4.18.4.2

Factor $2$ out of $- 2$ .

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

Step 4.18.4.3

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

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

Step 4.18.4.4

Cancel the common factors.

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Step 4.18.4.4.1

Factor $2$ out of $2$ .

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

Step 4.18.4.4.2

Cancel the common factor.

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

Step 4.18.4.4.3

Rewrite the expression.

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

Step 4.18.4.4.4

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

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

Step 4.18.5

Apply the distributive property.

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

Step 4.18.6

Multiply $- 1$ by $- 1$ .

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

Step 4.19

Add $2$ and $1$ .

$\arctan (- \sqrt{3 - \sqrt{2} - \sqrt{2}})$

Step 4.20

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

$\arctan (- \sqrt{3 - 2 \sqrt{2}})$

Step 5

The result can be shown in multiple forms.

Exact Form:

$\arctan (- \sqrt{3 - 2 \sqrt{2}})$

Decimal Form:

$- 0.39269908 \dots$