In an isosceles triangle, the apex angle opposite the base = 40 degrees. Find the angle at the base.

We know that in an isosceles triangle, the apex angle is 40 °. In order to find the angle at the base, let’s recall the theorem on the sum of the angles of a triangle and the properties of the angles at the base of an isosceles triangle.

The triangle sum theorem says that the sum of the angles of a triangle is 180 °.

In an isosceles triangle, the angles at the base are equal.

Let us first find the sum of the angles of the triangle at the base.

180 ° – 40 ° = 140 °.

We only have to divide the obtained values ​​by 2:

140 °: 2 = 70 ° base angle.