Exercise 32 Page 380

In the previous exercise, we found that m∠ ACB=136^(∘). We can also see that AC≅ BC by the markings.

Thus, △ ACB is isosceles. In this case, we should consider the Isosceles Triangle Theorem. If two sides of a triangle are congruent, then the angles opposite those sides are congruent. Using the theorem, let's show the congruent angles.

As we can see, ∠ CAB ≅ ∠ ABC which means that m∠ CAB = m∠ ABC. Using this equality, let's find m∠ ABC by the Interior Angles Theorem.

Thus, m∠ ABC is 22^(∘).