Trigonometry Examples

$\cos (θ) = - 0.8$

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.

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

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.

$Opposite = - \sqrt{{(1)}^{2} - {(- 0.8)}^{2}}$

Step 4

Simplify inside the radical.

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Step 4.1

Negate $\sqrt{{(1)}^{2} - {(- 0.8)}^{2}}$ .

Opposite $= - \sqrt{{(1)}^{2} - {(- 0.8)}^{2}}$

Step 4.2

One to any power is one.

Opposite $= - \sqrt{1 - {(- 0.8)}^{2}}$

Step 4.3

Raise $- 0.8$ to the power of $2$ .

Opposite $= - \sqrt{1 - 1 \cdot 0.64}$

Step 4.4

Multiply $- 1$ by $0.64$ .

Opposite $= - \sqrt{1 - 0.64}$

Step 4.5

Subtract $0.64$ from $1$ .

Opposite $= - \sqrt{0.36}$

Step 4.6

Rewrite $0.36$ as ${0.6}^{2}$ .

Opposite $= - \sqrt{{0.6}^{2}}$

Step 4.7

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

Opposite $= - 1 \cdot 0.6$

Step 4.8

Multiply $- 1$ by $0.6$ .

Opposite $= - 0.6$

Step 5

Find the value of sine.

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Step 5.1

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

$\sin (θ) = \frac{opp}{hyp}$

Step 5.2

Substitute in the known values.

$\sin (θ) = \frac{- 0.6}{1}$

Step 5.3

Divide $- 0.6$ by $1$ .

$\sin (θ) = - 0.6$

Step 6

Find the value of tangent.

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Step 6.1

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

$\tan (θ) = \frac{opp}{adj}$

Step 6.2

Substitute in the known values.

$\tan (θ) = \frac{- 0.6}{- 0.8}$

Step 6.3

Divide $- 0.6$ by $- 0.8$ .

$\tan (θ) = 0.75$

Step 7

Find the value of cotangent.

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Step 7.1

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

$\cot (θ) = \frac{adj}{opp}$

Step 7.2

Substitute in the known values.

$\cot (θ) = \frac{- 0.8}{- 0.6}$

Step 7.3

Divide $- 0.8$ by $- 0.6$ .

$\cot (θ) = 1.\overline{3}$

Step 8

Find the value of secant.

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Step 8.1

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

$\sec (θ) = \frac{hyp}{adj}$

Step 8.2

Substitute in the known values.

$\sec (θ) = \frac{1}{- 0.8}$

Step 8.3

Divide $1$ by $- 0.8$ .

$\sec (θ) = - 1.25$

Step 9

Find the value of cosecant.

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Step 9.1

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

$\csc (θ) = \frac{hyp}{opp}$

Step 9.2

Substitute in the known values.

$\csc (θ) = \frac{1}{- 0.6}$

Step 9.3

Divide $1$ by $- 0.6$ .

$\csc (θ) = - 1.\overline{6}$

Step 10

This is the solution to each trig value.

$\sin (θ) = - 0.6$

$\cos (θ) = - 0.8$

$\tan (θ) = 0.75$

$\cot (θ) = 1.\overline{3}$

$\sec (θ) = - 1.25$

$\csc (θ) = - 1.\overline{6}$