Introduction

A closed figure formed by the intersection of three non-parallel lines is called a triangle (Δ). 

On the basis of the length of sides, Triangle can be classified as 

1) Scalene Triangle: All three sides have different lengths.

2) Isosceles Triangle: Any two sides have equal length.

3) Equilateral Triangle: All three sides have equal lengths.

On the basis of Angles, Triangles can be classified as 

1) Acute-Angled Triangle: All the angles are between 0° and 90°.

2) Obtuse-Angled Triangle: One of the angles is between 90° and 180°.

3) Right-Angled Triangle: One of the angles is 90°.

1) The sum of all the three angles of a triangle is 180°.

2) The sum of the length of any two sides of a triangle is always greater than the length of the third side.

3) The difference between any two sides of a triangle is always less than the length of the third side.

4) The side opposite to the greater angle is the longer side of a triangle in comparison to the side opposite to the smaller angle.

5) The exterior angle of a triangle is always equal to the sum of the interior opposite angles, also known as the exterior angle property of a triangle.

6) The sum of all the exterior angles of a triangle is 360°.