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.

Question

Revolt · Accepted Answer

We know that m∠ZAB + m∠CAB = 180° by the .:

angle addition postulate

We also know m∠CAB + m∠ACB + m∠CBA = 180° because .:

of the triangle angle sum theorem

Therefore, we conclude m∠ZAB = m∠ACB + m∠CBA using the .:

subtraction property

Triangle Angle Theorems

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.

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