McGraw Hill Glencoe Algebra 2, 2012
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McGraw Hill Glencoe Algebra 2, 2012 View details
4. Law of Sines
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Exercise 5 Page 818

The Law of Sines relates the sine of each angle to the length of the opposite side.

E = 107^(∘)
d ≈ 7.9
f ≈ 7.0

Practice makes perfect

For any △ ABC, let the lengths of the sides opposite angles A, B, and C be a, b, and c, respectively.

The Law of Sines relates the sine of each angle to the length of the opposite side. sin A/a=sin B/b=sin C/c Let's start by finding m∠ E. Then, we will use the above law to find the values of d and f. We will find them one at a time.

Finding E

Consider the given triangle.

From the Triangle Angle Sum Theorem we know that the sum of the angles in a triangle is equal to 180^(∘). With this information we can find E. m ∠ E + 39^(∘) + 34^(∘) = 180^(∘) ⇕ m∠ E = 107^(∘)

Finding d

Let's mark the measure of the angle E on the graph.

We know that the length of a side is 12 and that the measure of its opposite angle is 107^(∘). We also know that the measure of the angle that is opposite to the side we want to find is 39^(∘). With this information and using the Law of Sines, we can write an equation in terms of d. sin 39^(∘)/d=sin 107^(∘)/12 Let's solve the above equation for d using the Cross Product Property.
sin 39^(∘)/d = sin 107^(∘)/12
sin 39^(∘)* 12 = sin 107^(∘)* d
sin 39^(∘)* 12/sin 107^(∘) = d
d = sin 39^(∘)* 12/sin 107^(∘)
d = 7.896901...
d ≈ 7.9

Finding f

Consider the given triangle with the new information.

We know that the length of a side is 12 and that the measure of its opposite angle is 107^(∘). We want to find the length of the side that is opposite to the angle whose measure is 34^(∘). We can use the Law of Sines again! sin 107^(∘)/12=sin 34^(∘)/f Let's solve the above equation for f using the Cross Product Property.
sin 107^(∘)/12=sin 34^(∘)/f
sin 107^(∘)* f = sin 34^(∘)* 12
f = sin 34^(∘)* 12/sin 107^(∘)
f = 7.016920...
f ≈ 7.0