Question

triangle abc, shown in the diagram below, is an isosceles triangle. $overline{ab}congoverline{ac}$. what is the measure, in degrees, of $angle abc$? 123° 43° 84° 57°

Explanation:

Step1: Find ∠ACB

Since ∠ACD = 123° and ∠ACB + ∠ACD=180° (linear - pair of angles), then ∠ACB = 180° - 123° = 57°.

Step2: Use isosceles - triangle property

In isosceles triangle ABC with AB = AC, ∠ABC=∠ACB. So ∠ABC = 57°.

Answer:

57°