Precalculus Examples

$\cos (x) = \frac{15}{17}$

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.

$\cos (x) = \frac{adjacent}{hypotenuse}$

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.

$Opposite = \sqrt{{(17)}^{2} - {(15)}^{2}}$

Step 4

Simplify inside the radical.

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Step 4.1

Raise $17$ to the power of $2$ .

Opposite $= \sqrt{289 - {(15)}^{2}}$

Step 4.2

Raise $15$ to the power of $2$ .

Opposite $= \sqrt{289 - 1 \cdot 225}$

Step 4.3

Multiply $- 1$ by $225$ .

Opposite $= \sqrt{289 - 225}$

Step 4.4

Subtract $225$ from $289$ .

Opposite $= \sqrt{64}$

Step 4.5

Rewrite $64$ as $8^{2}$ .

Opposite $= \sqrt{8^{2}}$

Step 4.6

Pull terms out from under the radical, assuming positive real numbers.

Opposite $= 8$

Step 5

Find the value of sine.

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Step 5.1

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

$\sin (x) = \frac{opp}{hyp}$

Step 5.2

Substitute in the known values.

$\sin (x) = \frac{8}{17}$

Step 6

Find the value of tangent.

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Step 6.1

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

$\tan (x) = \frac{opp}{adj}$

Step 6.2

Substitute in the known values.

$\tan (x) = \frac{8}{15}$

Step 7

Find the value of cotangent.

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Step 7.1

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

$\cot (x) = \frac{adj}{opp}$

Step 7.2

Substitute in the known values.

$\cot (x) = \frac{15}{8}$

Step 8

Find the value of secant.

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Step 8.1

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

$\sec (x) = \frac{hyp}{adj}$

Step 8.2

Substitute in the known values.

$\sec (x) = \frac{17}{15}$

Step 9

Find the value of cosecant.

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Step 9.1

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

$\csc (x) = \frac{hyp}{opp}$

Step 9.2

Substitute in the known values.

$\csc (x) = \frac{17}{8}$

Step 10

This is the solution to each trig value.

$\sin (x) = \frac{8}{17}$

$\cos (x) = \frac{15}{17}$

$\tan (x) = \frac{8}{15}$

$\cot (x) = \frac{15}{8}$

$\sec (x) = \frac{17}{15}$

$\csc (x) = \frac{17}{8}$