Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
7. Law of Sines and Law of Cosines
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Exercise 18 Page 513

Use the Law of Sines.

m ∠ C = 90^(∘)
a ≈ 17.5
b ≈ 39.3

Practice makes perfect

We need to solve the given triangle. Let's begin by color coding the opposite angles and sides. We will also call the unknown sides a and b. It will help us use the Law of Sines later.

Let's find the measure of ∠ C, and side lengths b and a one at a time.

Finding m ∠ C

To find m ∠ C we can use the Triangle Sum Theorem. This tells us that the measures of the angles in a triangle add up to 180.

24^(∘) + 66^(∘) + m ∠ C = 180^(∘) ⇕ m ∠ C = 90^(∘)

Finding the Side Length b

To find the side length b of the given triangle, we can use the Law of Sines. b/sin B = c/sin C Let's substitute c= 43, m ∠ B = 66^(∘), and m ∠ C = 90^(∘) to calculate b.
b/sin B = c/sin C
b/sin 66^(∘) = 43/sin 90^(∘)
b =43 sin 66^(∘)/sin 90^(∘)
b = 39.282454...
b ≈ 39.3

Finding the Side Length a

We found that the given triangle is a right triangle. Therefore, we can use the Pythagorean Theorem to find the side length a of the given triangle. In our triangle, a and b are the legs and c is the hypotenuse of a right triangle. We are given a triangle with b≈ 39.3 and c= 43. Let's substitute these values into the formula.
a^2+b^2=c^2
a^2+ 39.3^2= 43^2
Solve for a
a^2+1544.49=1849
a^2=304.51
a=sqrt(304.51)
a=17.450214...
a ≈ 17.5
Since a negative side length does not make sense, we only need to consider positive solutions.

Completing the Triangle

With all of the angle measures and side lengths, we can complete our diagram.