The two triangles now formed with altitude as its common side can be proved congruent by SSS congruence followed by proving the angles opposite to the equal sides to be equal by CPCT. An isosceles triangle can be drawn, followed by constructing its altitude. Isosceles triangle theorem can be proved by using the congruence properties and properties of an isosceles triangle.

Isosceles triangle theorem states that, if two sides of an isosceles triangle are equal then the angles opposite to the equal sides will also have the same measure. Related ArticlesĬheck these articles related to the concept of the isosceles triangle theorem.įAQs on Isosceles Triangle Theorem What is Isosceles Triangle Theorem? Hence we have proved that, if two angles of a triangle are congruent, then the sides opposite to the congruent angles are equal. Proof: We know that the altitude of a triangle is always at a right angle with the side on which it is dropped. Construction: Altitude AD from vertex A to the side BC. Let's draw a triangle with two congruent angles as shown in the figure below with the markings as indicated. Converse of Isosceles Triangle Theorem Proof We will be using the properties of the isosceles triangle to prove the converse as discussed below. This is exactly the reverse of the theorem we discussed above. The converse of isosceles triangle theorem states that if two angles of a triangle are congruent, then the sides opposite to the congruent angles are equal. Hence, we have proved that if two sides of a triangle are congruent, then the angles opposite to the congruent sides are equal. Proof: We know, that the altitude of an isosceles triangle from the vertex is the perpendicular bisector of the third side. Given: ∆ABC is an isosceles triangle with AB = AC. Let's draw an isosceles triangle with two equal sides as shown in the figure below. To understand the isosceles triangle theorem, we will be using the properties of an isosceles triangle for the proof as discussed below.

Isosceles triangle theorem states that if two sides of a triangle are congruent, then the angles opposite to the congruent sides are also congruent.

Isosceles right angle triangle