In an isosceles triangle, the apex angle is 2 times the base angle. Find the corners of a triangle

Let ABC be an isosceles triangle, angle A = angle C – the angles at the base, angle B – the angle at the apex.
Let’s denote angle A as x, then angle A = angle C = x, and angle B = 2x (since, by condition, the angle at the apex is 2 times greater than the angle at the base).
By the theorem on the sum of the angles of a triangle:
angle A + angle B + angle C = 180 degrees;
x + 2x + x = 180;
4x = 180;
x = 180/4;
x = 45.
Angle A = angle C = x = 45 degrees, angle B = 2x = 2 * 45 = 90 degrees.
Answer: angle A = 45 degrees, angle B = 90 degrees, angle C = 45 degrees.