Notes On Properties of Triangles - CBSE Class 9 Maths

A triangle is said to be an isosceles triangle if two of its sides are equal. The third side of the triangle is called the  base. The median from the vertex to the base is perpendicular to the base and divides the triangle into two congruent right angled triangles.

Angles opposite to equal sides of an isosceles triangle are equal.

In ΔABC, if the sides AB = AC, then  ∠B = ∠C.

The sides opposite to equal angles of a triangle are equal.
In ΔABC, if the angles ∠B = ∠C, then AB = AC.

The three angles of an equilateral triangle are equal.

Summary

A triangle is said to be an isosceles triangle if two of its sides are equal. The third side of the triangle is called the  base. The median from the vertex to the base is perpendicular to the base and divides the triangle into two congruent right angled triangles.

Angles opposite to equal sides of an isosceles triangle are equal.

In ΔABC, if the sides AB = AC, then  ∠B = ∠C.

The sides opposite to equal angles of a triangle are equal.
In ΔABC, if the angles ∠B = ∠C, then AB = AC.

The three angles of an equilateral triangle are equal.

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