Trigonometry Examples

$\sec (\frac{- 21 π}{4})$

Step 1

Move the negative in front of the fraction.

$\sec (- \frac{21 π}{4})$

Step 2

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

$\sec (\frac{3 π}{4})$

Step 3

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because secant is negative in the second quadrant.

$- \sec (\frac{π}{4})$

Step 4

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

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

Step 5

Multiply $\frac{2}{\sqrt{2}}$ by $\frac{\sqrt{2}}{\sqrt{2}}$ .

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

Step 6

Combine and simplify the denominator.

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Step 6.1

Multiply $\frac{2}{\sqrt{2}}$ by $\frac{\sqrt{2}}{\sqrt{2}}$ .

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

Step 6.2

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

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

Step 6.3

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

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

Step 6.4

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

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

Step 6.5

Add $1$ and $1$ .

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

Step 6.6

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

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Step 6.6.1

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

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

Step 6.6.2

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

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

Step 6.6.3

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

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

Step 6.6.4

Cancel the common factor of $2$ .

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Step 6.6.4.1

Cancel the common factor.

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

Step 6.6.4.2

Rewrite the expression.

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

Step 6.6.5

Evaluate the exponent.

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

Step 7

Cancel the common factor of $2$ .

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Step 7.1

Cancel the common factor.

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

Step 7.2

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

$- \sqrt{2}$

Step 8

The result can be shown in multiple forms.

Exact Form:

$- \sqrt{2}$

Decimal Form:

$- 1.41421356 \dots$