Base angles

An isosceles triangle is a triangle with two sides of equal length. The two equal sides are called the legs and the third side is called the base. 

The angles at the base are called the base angles, and the angle opposite the base is called the vertex angle.

In an isosceles triangle, the apex is the vertex where the two sides of equal length meet, opposite the unequal third side.

AC = BC

∠A = ∠B = (180º – ∠C) : 2

∠C = 180º -∠A – ∠B  =180 º – (∠A + ∠B)