The angle at the base of an isosceles triangle is 75% of the angle at its apex. Find the angle at the apex.

1. Vertices of triangle A, B, C. С.A is 75% ∠B.

2. ∠A = 0.75∠B.

3.∠A = ∠C = 0.75∠B (angles located on one side of the triangle, which is

isosceles, are equal).

4.Considering that the total value of the angles of the specified geometric figure is

180 °, we calculate the degree measure ∠В:

∠В = 180 – 0.75∠В – 0.75∠В.

2.5∠H = 180 °

∠В = 72 °

Answer: ∠В is equal to 72 °