Question

what theorem can be used alone to find the measure of ∠a in △ab the supplementary angle theorem the exterior angle theorem the triangle sum theorem the pythagorean theorem

Explanation:

The Exterior Angle Theorem states that an exterior angle of a triangle is equal to the sum of the two non - adjacent interior angles. In this case, \(\angle ACD\) (the exterior angle) is equal to \(\angle A+\angle B\). So, we can use the Exterior Angle Theorem to find \(\angle A\) since \(\angle A=\angle ACD - \angle B\).

Answer:

the Exterior Angle Theorem