Exercise 29 Page 380

Looking at the given figure, we can figure out that AD≅ DC.

Thus, △ ADC 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, ∠ CAD ≅ ∠ ACD which means that m∠ CAD = m∠ ACD. Using this equality, let's find m∠ CAD by the Interior Angles Theorem.