In the above given figure, we see that the length of two sides P and Q when added then it is less than the length of O because it violets the definition of triangle inequalities, inequalities of Triangles theorem. We know that the triangle has equal sides, and the angle which is opposite to these sides are also equal. In a triangle if two sides are not equal than the sum of angles opposite to these sides are also not equal. And the angle which is larger is just opposite the larger side.

Other theorem that if two angles in a triangle is not equal then the sum of all the sides opposite these angles are also not equal. Then the larger side is just opposite to the larger angles.

A packed figure consisting of three line segment which is linked end- to- end is known as triangles. Triangles have vertex, base, altitude, median, area, perimeter, interior angles, and exterior angles.

Three vertices are present in a triangle. Out of three sides one side can be taken as base of a triangle. Mostly we will use reference side because it is used in calculating the area of a triangle. And the perpendicular from the base to the opposite side vertex is Altitude of a triangle. And a line from the vertex of a triangle to the mid Point of the opposite sides is a Median of a triangle. There are seven types of triangle which are isosceles, equilateral, scalene, right triangle, obtuse, acute and equiangular.