In an isosceles triangle that has exactly two equal sides, the equal sides are called legs and the third side is called the base. The angle included by the legs is called the vertex angle and the angles that have the base as one of their sides are called the base angles. The vertex opposite the base is called the apex.

What is the rule for an isosceles triangle?

The rule for an isosceles triangle is that the triangle must have two sides of equal length. These two sides are called the legs of the triangle and the unequal side is called the base. The isosceles triangle theorem further states that the angles opposite to each of the equal sides must also be equal.

How do you prove that a triangle is isosceles?

Explanation: One way of proving that it is an isosceles triangle is by calculating the length of each side since two sides of equal lengths means that it is an isosceles triangle.