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∘ Applying the concept that says that angles on a straight line add up to 180∘ ⇒x+56=180 Make x the subject ⇒x=180−56 x=124