Triangle ABC is isosceles AC = BC Angle A is 80 degrees Find angle C

So, we are given a triangle ABC isosceles, AC = BC. It is also known that the angle A is equal to 80 °. In order to find the angle C, we will use the theorem on the sum of the angles of a triangle and the properties of the angles at the base of an isosceles triangle.

So angle C is the angle at the apex of an isosceles triangle, and angles A and B are angles at the base.

The angles at the base of an isosceles triangle are equal to each other, that is, angle A is equal to angle B and equal to 80 °.

Looking for corner C:

180 ° – (80 ° + 80 °) = 180 ° – 160 ° = 20 °