The angle at the base of an isosceles triangle is 71 °. What is the angle at the top.

It is known from the condition that the angle at the base of an isosceles triangle is 71 °. In order to find the value of the angle at the vertices of the triangle, we will use the properties of the angles at the base of an isosceles triangle and the theorem on the sum of the angles of a triangle.

So, the angles at the base of an isosceles triangle are equal to each other. And the theorem on the sum of the angles of a triangle says that the sum of the angles of a triangle is 180 °.

180 ° – 71 ° * 2 = 180 ° – 142 ° = 38 °.

Answer: the angle at the apex of an isosceles triangle is 38 °.