Trigonometry Examples

$\cos (2 A) = \frac{- 2}{3}$

Step 1

Use the definition of cosine to find the known sides of the unit circle right triangle. The quadrant determines the sign on each of the values.

$\cos (2 A) = \frac{adjacent}{hypotenuse}$

Step 2

Find the opposite side of the unit circle triangle. Since the adjacent side and hypotenuse are known, use the Pythagorean theorem to find the remaining side.

$Opposite = - \sqrt{{hypotenuse}^{2} - {adjacent}^{2}}$

Step 3

Replace the known values in the equation.

$Opposite = - \sqrt{{(3)}^{2} - {(- 2)}^{2}}$

Step 4

Simplify inside the radical.

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Step 4.1

Negate $\sqrt{{(3)}^{2} - {(- 2)}^{2}}$ .

Opposite $= - \sqrt{{(3)}^{2} - {(- 2)}^{2}}$

Step 4.2

Raise $3$ to the power of $2$ .

Opposite $= - \sqrt{9 - {(- 2)}^{2}}$

Step 4.3

Raise $- 2$ to the power of $2$ .

Opposite $= - \sqrt{9 - 1 \cdot 4}$

Step 4.4

Multiply $- 1$ by $4$ .

Opposite $= - \sqrt{9 - 4}$

Step 4.5

Subtract $4$ from $9$ .

Opposite $= - \sqrt{5}$

Step 5

Find the value of sine.

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Step 5.1

Use the definition of sine to find the value of $\sin (2 A)$ .

$\sin (2 A) = \frac{opp}{hyp}$

Step 5.2

Substitute in the known values.

$\sin (2 A) = \frac{- \sqrt{5}}{3}$

Step 5.3

Move the negative in front of the fraction.

$\sin (2 A) = - \frac{\sqrt{5}}{3}$

Step 6

Move the negative in front of the fraction.

$\cos (2 A) = - \frac{2}{3}$

Step 7

Find the value of tangent.

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Step 7.1

Use the definition of tangent to find the value of $\tan (2 A)$ .

$\tan (2 A) = \frac{opp}{adj}$

Step 7.2

Substitute in the known values.

$\tan (2 A) = \frac{- \sqrt{5}}{- 2}$

Step 7.3

Dividing two negative values results in a positive value.

$\tan (2 A) = \frac{\sqrt{5}}{2}$

Step 8

Find the value of cotangent.

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Step 8.1

Use the definition of cotangent to find the value of $\cot (2 A)$ .

$\cot (2 A) = \frac{adj}{opp}$

Step 8.2

Substitute in the known values.

$\cot (2 A) = \frac{- 2}{- \sqrt{5}}$

Step 8.3

Simplify the value of $\cot (2 A)$ .

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Step 8.3.1

Dividing two negative values results in a positive value.

$\cot (2 A) = \frac{2}{\sqrt{5}}$

Step 8.3.2

Multiply $\frac{2}{\sqrt{5}}$ by $\frac{\sqrt{5}}{\sqrt{5}}$ .

$\cot (2 A) = \frac{2}{\sqrt{5}} \cdot \frac{\sqrt{5}}{\sqrt{5}}$

Step 8.3.3

Combine and simplify the denominator.

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Step 8.3.3.1

Multiply $\frac{2}{\sqrt{5}}$ by $\frac{\sqrt{5}}{\sqrt{5}}$ .

$\cot (2 A) = \frac{2 \sqrt{5}}{\sqrt{5} \sqrt{5}}$

Step 8.3.3.2

Raise $\sqrt{5}$ to the power of $1$ .

$\cot (2 A) = \frac{2 \sqrt{5}}{\sqrt{5} \sqrt{5}}$

Step 8.3.3.3

Raise $\sqrt{5}$ to the power of $1$ .

$\cot (2 A) = \frac{2 \sqrt{5}}{\sqrt{5} \sqrt{5}}$

Step 8.3.3.4

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

$\cot (2 A) = \frac{2 \sqrt{5}}{{\sqrt{5}}^{1 + 1}}$

Step 8.3.3.5

Add $1$ and $1$ .

$\cot (2 A) = \frac{2 \sqrt{5}}{{\sqrt{5}}^{2}}$

Step 8.3.3.6

Rewrite ${\sqrt{5}}^{2}$ as $5$ .

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Step 8.3.3.6.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{5}$ as $5^{\frac{1}{2}}$ .

$\cot (2 A) = \frac{2 \sqrt{5}}{{(5^{\frac{1}{2}})}^{2}}$

Step 8.3.3.6.2

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

$\cot (2 A) = \frac{2 \sqrt{5}}{5^{\frac{1}{2} \cdot 2}}$

Step 8.3.3.6.3

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

$\cot (2 A) = \frac{2 \sqrt{5}}{5^{\frac{2}{2}}}$

Step 8.3.3.6.4

Cancel the common factor of $2$ .

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Step 8.3.3.6.4.1

Cancel the common factor.

$\cot (2 A) = \frac{2 \sqrt{5}}{5^{\frac{2}{2}}}$

Step 8.3.3.6.4.2

Rewrite the expression.

$\cot (2 A) = \frac{2 \sqrt{5}}{5}$

Step 8.3.3.6.5

Evaluate the exponent.

$\cot (2 A) = \frac{2 \sqrt{5}}{5}$

Step 9

Find the value of secant.

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Step 9.1

Use the definition of secant to find the value of $\sec (2 A)$ .

$\sec (2 A) = \frac{hyp}{adj}$

Step 9.2

Substitute in the known values.

$\sec (2 A) = \frac{3}{- 2}$

Step 9.3

Move the negative in front of the fraction.

$\sec (2 A) = - \frac{3}{2}$

Step 10

Find the value of cosecant.

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Step 10.1

Use the definition of cosecant to find the value of $\csc (2 A)$ .

$\csc (2 A) = \frac{hyp}{opp}$

Step 10.2

Substitute in the known values.

$\csc (2 A) = \frac{3}{- \sqrt{5}}$

Step 10.3

Simplify the value of $\csc (2 A)$ .

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Step 10.3.1

Move the negative in front of the fraction.

$\csc (2 A) = - \frac{3}{\sqrt{5}}$

Step 10.3.2

Multiply $\frac{3}{\sqrt{5}}$ by $\frac{\sqrt{5}}{\sqrt{5}}$ .

$\csc (2 A) = - (\frac{3}{\sqrt{5}} \cdot \frac{\sqrt{5}}{\sqrt{5}})$

Step 10.3.3

Combine and simplify the denominator.

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Step 10.3.3.1

Multiply $\frac{3}{\sqrt{5}}$ by $\frac{\sqrt{5}}{\sqrt{5}}$ .

$\csc (2 A) = - \frac{3 \sqrt{5}}{\sqrt{5} \sqrt{5}}$

Step 10.3.3.2

Raise $\sqrt{5}$ to the power of $1$ .

$\csc (2 A) = - \frac{3 \sqrt{5}}{\sqrt{5} \sqrt{5}}$

Step 10.3.3.3

Raise $\sqrt{5}$ to the power of $1$ .

$\csc (2 A) = - \frac{3 \sqrt{5}}{\sqrt{5} \sqrt{5}}$

Step 10.3.3.4

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

$\csc (2 A) = - \frac{3 \sqrt{5}}{{\sqrt{5}}^{1 + 1}}$

Step 10.3.3.5

Add $1$ and $1$ .

$\csc (2 A) = - \frac{3 \sqrt{5}}{{\sqrt{5}}^{2}}$

Step 10.3.3.6

Rewrite ${\sqrt{5}}^{2}$ as $5$ .

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Step 10.3.3.6.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{5}$ as $5^{\frac{1}{2}}$ .

$\csc (2 A) = - \frac{3 \sqrt{5}}{{(5^{\frac{1}{2}})}^{2}}$

Step 10.3.3.6.2

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

$\csc (2 A) = - \frac{3 \sqrt{5}}{5^{\frac{1}{2} \cdot 2}}$

Step 10.3.3.6.3

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

$\csc (2 A) = - \frac{3 \sqrt{5}}{5^{\frac{2}{2}}}$

Step 10.3.3.6.4

Cancel the common factor of $2$ .

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Step 10.3.3.6.4.1

Cancel the common factor.

$\csc (2 A) = - \frac{3 \sqrt{5}}{5^{\frac{2}{2}}}$

Step 10.3.3.6.4.2

Rewrite the expression.

$\csc (2 A) = - \frac{3 \sqrt{5}}{5}$

Step 10.3.3.6.5

Evaluate the exponent.

$\csc (2 A) = - \frac{3 \sqrt{5}}{5}$

Step 11

This is the solution to each trig value.

$\sin (2 A) = - \frac{\sqrt{5}}{3}$

$\cos (2 A) = - \frac{2}{3}$

$\tan (2 A) = \frac{\sqrt{5}}{2}$

$\cot (2 A) = \frac{2 \sqrt{5}}{5}$

$\sec (2 A) = - \frac{3}{2}$

$\csc (2 A) = - \frac{3 \sqrt{5}}{5}$