One of the angles of an isosceles triangle ABC is equal to 100 degrees. Find any other corner

The angles of any triangle add up to 180 degrees.

In an isosceles triangle, the two angles are equal.

Suppose that a triangle ABC with angles A, B, C and whose angle is A = C according to the condition of the problem.

Let’s make the first guess:

Let the angle A be equal to 100 degrees, then the angle C is also equal to 100 degrees, but a contradiction arises, the sum of the angles of the triangle cannot be more than 180 degrees (A + C already gives us 200).

Let’s make a second guess:

Let the angle B be 100 degrees.

Let’s count how many degrees are at the corners A and C:

180 – 100 = 80.

Because angles A, C are equal then each of these angles is equal to 40 degrees.

Answer: A = 40, B = 100, C = 40 degrees.