Question

We start with triangle ABC and see that angle ZAB is an exterior angle created by the extension of side AC. Angles ZAB and CAB are a linear pair by definition. We know that m∠ZAB + m∠CAB = 180° by the . We also know m∠CAB + m∠ACB + m∠CBA = 180° because .

Answer 1

The first answer is: definition of complementary angles.

The second is: of the triangle sum theorem.

The third one is: substraction property