Answer the given questions about the indicated examples of this section.

In Example 2, if ∠1 = 70° and ∠5 = 45° in Fig. 2.25, what is the measure of ∠2?

Data from Example 2

Fig. 2.25, because ∠1, ∠2, and ∠3 constitute a straight angle, ∠1 + ∠2 + ∠3 = 180°

Also, by noting alternate interior angles, we see that ∠1 = ∠4 and ∠3 = ∠5.

Therefore, by substitution, we have ∠4 + ∠2 + ∠5 = 180°

Therefore, if two of the angles of a triangle are known, the third may be found by subtracting the sum of the first two from 180°.

A D 2 3 5, Fig. 2.25 C AB || EC B