Concepts A triangle which has two of its sides equal is called an isosceles triangle Properties of Isosceles Triangle 1. The two equal sides of an isosceles triangle are called the legs and the angle between them is called the vertex angle or apex angle. 2. The side opposite the vertex angle is called the base and base angles are equal. 3. The perpendicular from the vertex angle bisects the base and the vertex angle. Applying property 2 to redraw the triangle in the question gives us the diagram below: From the above properties, you will realize that angle CBA=BAC=56∘ Considering the basic properties of angles in a triangle below: Applying the concept which says that the sum of all the angles in a triangle should be 180∘ ⇒56+y+56=180 y+56+56=180 y+112=180 ⇒y=180−112 y=68∘