# Math՚s: Lines and Angles: Triangle: Meaning, Types and Properties (For CBSE, ICSE, IAS, NET, NRA 2022)

Get unlimited access to the best preparation resource for CBSE/Class-10 : get questions, notes, tests, video lectures and more- for all subjects of CBSE/Class-10.

## 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