Big Ideas Math: Modeling Real Life, Grade 8
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Big Ideas Math: Modeling Real Life, Grade 8 View details
2. Angles of Triangles
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Exercise 7 Page 115

When using a protractor, remember that you should place it at the vertex of the angle.

∠ A=30^(∘), ∠ B=105^(∘), ∠ C=45^(∘), ∠ D=150^(∘), ∠ E=75^(∘), ∠ F=105^(∘), ∠ G=30^(∘)

Practice makes perfect

We are given a diagram of two parallel lines and two transversals. We want to find the measures of the labeled angles.

To measure an angle, we can use a protractor. To do this, we place the middle of the base of the protractor at the vertex of the angle. Then, we align one of the rays of the angle with the segment marked 0 on the protractor.

The other ray of the angle marks the angle's measure on the protractor. Using this method, we can measure ∠ A on our diagram.

finding the measure of angle a

The measure of ∠ A is 30^(∘). In similar way, we can find the measures of other labeled angles.

finding the measure of other labeled angles

We found that the measure of ∠ B is 105^(∘), ∠ C is 45^(∘), ∠ D is 150^(∘), ∠ E is 75^(∘), ∠ F is 105^(∘), and ∠ G is 30^(∘).

Extra

Conclusions
We found the measures of all labeled angles. Recall that when a transversal intersects parallel lines, it creates alternate interior angles are congruent. Let's look at the given diagram once again!

As we can see, there are two pairs of alternate interior angles. Notice that one pair of these angles measures 30^(∘) and the second pair measures 105^(∘). This means that we correctly used the protractor to measure these angles.