# Math's: Lines and Angles: Triangle: Meaning, Types and Properties

Get unlimited access to the best preparation resource for CBSE/Class-12 Business-Studies: fully solved questions with step-by-step explanation- practice your way to success.

Download PDF of This Page (Size: 258K) ↧

## Triangle- Meaning

A triangle is a closed figure formed on a plane by joining three collinear points by three-line segments. It has six elements-

Three angles formed on the three points. ∠A, ∠B and ∠C in the given figure.

Three sides that consist of the three-line segments. AB, BC and AC in the given figure.

## Types of Triangles

**Triangles can be classified into different types on two bases-**

### On the Basis of Sides

**Equilateral triangle:**A triangle in which all the three sides are equal is called an equilateral triangle.**Isosceles triangle:**A triangle in which two sides are equal is called an isosceles triangle.**Scalene triangle:**A triangle in which all sides are of different lengths, is called a scalene triangle

### On the Basis of Angles

**Obtuse angled triangle:**A triangle in which one of the angles is an obtuse angle is called an obtuse angled triangle or simply obtuse triangle.**Right angled triangle:**A triangle in which one of the angles is a right angle is called a right-angled triangle or right triangle.**Acute angled triangle:**A triangle in which all the three angles are acute is called an acute angled triangle or acute triangle.

## Properties of Triangles

Angle Sum Property of a Triangle- The sum of all the three angles of a triangle is . Thus, in ,

The angle formed by a side of the triangle produced and another side of the triangle is called an exterior angle of the triangle. Corresponding to an exterior angle of a triangle, there are two interior opposite angles. Interior opposite angles are the angles of the triangle not forming a linear pair with the given exterior angle.

An exterior angle of a triangle is equal to the sum of the two interior opposite angles. In