In triangle ABC, the outside angle at vertex B is 124 °, AC = BC. Find the degree measure for angle C.

It is known:

Triangle ABC;
Outside angle at apex B is equal to 124 °;
AC = BC;
Find corner C.

One angle in an isosceles triangle is already known, then we can find 2 second angles.

If the outside angle B is 124 °, then the inside angle of the triangle is 180 ° – 124 ° = 56 °.

Since the triangle is isosceles, then the angle A = angle B = 56 °.

Since the sum of all the angles of the triangle is 180 °, then the angle C is equal to:

Angle С = 180 ° – angle А – angle С = 180 ° – 56 ° – 56 ° = 180 ° – 112 ° = 68 °;

Answer: angle C = 68 °.