Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
6. Solving Right Triangles
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Exercise 28 Page 506

Solve one triangle at a time. Start with △ TUS.

m ∠ UTS = 26^(∘)
ST ≈ 9.1 m
TU ≈ 8.2 m
m ∠ VTW ≈ 39.7^(∘)
m ∠ TVW ≈ 50.3^(∘)
TW ≈ 10.9 m

Practice makes perfect

Let's analyze the given right triangles.

We will solve each right triangle separately. We will start with △ TUS.

△ TUS

We will find the missing measures one at a time. In this case, this means that we want to find m ∠ UTS, ST, and TU.

Angle Measure

Let's analyze △ TUS.

To find m∠ UTS, recall that the acute angles of a right triangle are complementary. Therefore, m ∠ UTS and m ∠ S add to 90. m ∠ UTS + m ∠ TSU = 90 Since m∠ TSU= 64, we can substitute this value in our equation and find the measure of ∠ UTS.

m ∠ UTS + 64 = 90 ⇔ m ∠ UTS = 26

Side Lengths

Let x be the length of ST. We can find its value by using the cosine ratio.

The cosine of ∠ TSU is the ratio of the length of the adjacent leg of ∠ TSU to the length of the hypotenuse. Cosine=Adjacent/Hypotenuse ⇒ cos 64^(∘) =4/x We can use the obtained equation to find x. We have to use a calculator to find the value of cos 64^(∘).
cos 64^(∘)=4/x
0.438371 ...= 4/x
(0.438371 ...)x = 4
x=9.124691 ...
x ≈ 9.1
Therefore, the measure of ST is 9.1 m, rounded to nearest tenth. Finally, we can find the measure of TU. To do it, we can use the Pythagorean Theorem. a^2+b^2=c^2 For our triangle, the lengths of one of the legs and the hypotenuse are 4 and 9.1, respectively. We want to find the length of the other leg, which is TU. Let's substitute these values in the above equation.
a^2+b^2=c^2
TU^2+ 4^2= 9.1^2
Solve for TU
(TU)^2+16=82.81
(TU)^2=66.81
TU=sqrt(66.81)
TU = 8.173738 ...
TU ≈ 8.2
We have found the measures of all the angles and the lengths of all the sides in △ TUS.

△ VTW

Since we already found the length of ST, we will first find the length of VT. VT=VS+ST ⇒ VT=5+9.1=14.1 As to the rest of the missing measures, we will find them one at a time. In this case, this means that we want to find m ∠ VTW, m ∠ TVW, and TW.

Angle Measures

Let's analyze △ VTW. We can find m ∠ VTW using the sine ratio.

The sine of ∠ VTW is the ratio of the length of the leg opposite ∠ VTW to the length of the hypotenuse. Sine=Opposite/Hypotenuse ⇒ sin ∠ VTW =9/14.1 By definition, the inverse sine of 9/14.1 is the measure of ∠ VTW. To find it, we have to use a calculator.
m∠ VTW=sin ^(-1) 9/14.1
m∠ VTW = 39.665022 ...
m ∠ VTW ≈ 39.7
To find m∠ TVW, recall that the acute angles of a right triangle are complementary. Therefore, m ∠ VTW and m ∠ TVW add to 90. m ∠ VTW + m ∠ TVW = 90 Now, we can substitute the measure of ∠ VTW in our equation and find the measure of ∠ TVW. 39.7+ m ∠ TVW = 90 ⇔ m ∠ TVW ≈ 50.3

Side Length

Finally, we can find the length of TW. To do it, we can use the Pythagorean Theorem. a^2+b^2=c^2 In this case, the lengths of one of the legs and the hypotenuse are 9 and 14.1, respectively. We want to find the length of the other leg, which is TW. Let's substitute these values in the above equation.
a^2+b^2=c^2
TW^2 + 9^2= 14.1^2
Solve for TW
(TW)^2+81=198.81
(TW)^2= 117.81
TW= sqrt(117.81)
TW ≈ 10.854032 ...
TW ≈ 10.9