Calculate the angles of an isosceles triangle if: a) the apex angle is 28 degrees; b) the angle at the base

Calculate the angles of an isosceles triangle if: a) the apex angle is 28 degrees; b) the angle at the base is 77 degrees, prove that all angles in an equilateral triangle are equal. What is the value of the angle of an equilateral triangle?

The problem says that the triangle is isosceles, then the base is based on two identical angles.
Since the angle at the vertex is 28 °, and the sum of the angles in the triangle is 180 °, the sum of the two angles adjacent to the base is: 180 – 28 = 152 °, then these angles are equal to 152/2 = 76 °.
Since the angle at the base is 77 °, the sum of the two angles is 77 + 77 = 154 °, then the angle at the top is: 180 – 154 = 26 °.