The angles at the base of an isosceles triangle add up to 90. Find the outer corners of this triangle.

The condition says that the sum of the angles at the base of an isosceles triangle is 90 °. In order to find the outer corners of this triangle, let’s first find the inner corners of the triangle.

So, the sum of the angles of a triangle is 180 °. We are looking for the degree measure of the third angle:

180 ° – 90 ° = 90 ° apex angle.

90 °: 2 = 45 ° angles at the base.

The sum of adjacent angles is 180 °.

180 ° – 90 ° = 90 ° outside angle at the apex of the triangle;

180 ° – 45 ° = 135 ° outside angles at each of their angles at the base of the triangle.