What are the angles of an isosceles right triangle?

Let ABC be an isosceles right-angled triangle, angle A = 90 degrees.
For a triangle to be considered isosceles, it is necessary that its two sides (lateral) and the angles at the third side (base) are equal. Then angle B = angle C = x.
By the theorem on the sum of the angles of a triangle:
angle A + angle B + angle C = 180 degrees;
90 + x + x = 180;
2x = 90;
x = 90/2;
x = 45 degrees.
Angle B = angle C = x = 45 degrees.
Answer: angle A = 90 degrees, angle B = 45 degrees, angle C = 45 degrees.