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Lesson 6: Modeling with right triangles

Right triangle trigonometry review

Review right triangle trigonometry and how to use it to solve problems.

What are the basic trigonometric ratios?

Want to learn more about sine, cosine, and tangent? Check out this video.

Trigonometry can be used to find a missing side length in a right triangle. Let's find, for example, the measure of

A C

in this triangle:

We are given the measure of angle

∠ B

and the length of the

hypotenuse

, and we are asked to find the side

opposite

∠ B

. The trigonometric ratio that contains both of those sides is the sine:

\begin{aligned} \sin (∠ B) & = \frac{A C}{A B} \\ \sin (40^{\circ}) & = \frac{A C}{7} ∠ B = 40^{\circ}, A B = 7 \\ 7 \cdot \sin (40^{\circ}) & = A C \end{aligned}

Now we evaluate using the calculator and round:

A C = 7 \cdot \sin (40^{\circ}) \approx 4.5

Problem 1.1

B C =

Round your answer to the nearest hundredth.

Want to try more problems like this? Check out this exercise.

Trigonometry can also be used to find missing angle measures. Let's find, for example, the measure of

∠ A

in this triangle:

We are given the length of the side

adjacent

to the missing angle, and the length of the

hypotenuse

. The trigonometric ratio that contains both of those sides is the cosine:

\begin{aligned} \cos (∠ A) & = \frac{A C}{A B} \\ \cos (∠ A) & = \frac{6}{8} A C = 6, A B = 8 \\ ∠ A & = \cos^{- 1} (\frac{6}{8}) \end{aligned}

Now we evaluate using the calculator and round:

∠ A = \cos^{- 1} (\frac{6}{8}) \approx {41.41}^{\circ}

Problem 2.1

∠ A =

^{\circ}

Round your answer to the nearest hundredth.

Want to try more problems like this? Check out this exercise.

Problem 3.1

Howard is designing a chair swing ride. The swing ropes are

5

meters long, and in full swing they tilt in an angle of

29^{\circ}

. Howard wants the chairs to be

2.75

meters above the ground in full swing.

How tall should the pole of the swing ride be?
Round your final answer to the nearest hundredth.

meters

Want to try more problems like this? Check out this exercise.

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