Triangle  Definition with Examples
In geometry, a triangle is a closed, twodimensional shape with three straight sides. A triangle is also a polygon.
We can find the shape of a triangle in a flag, the musical instrument triangle, and a roadside signboard.
To classify triangles according to their angles, we measure each of its interior angles. Triangles can be classified by angles, as:



An acute triangle has all interior angles acute (less than 90°), a right triangle has one right angle (equal to 90°) and an obtuse triangle has one obtuse angle (greater than 90°).
To classify the triangles according to their sides, we measure the length of each of its sides. Triangles can be classified by their sides, as:



To classify triangles according to both angles and sides, we measure the interior angles and length of the sides of the triangle. Few examples of triangles classified on the basis of both angles and sides are:



The angle sum property of a triangle states that all the interior angles of a triangle add up to 180 degrees.
Based on the measure of their sides, there are 3 types of triangles: 1. Equilateral Triangle (all 3 sides are equal) 2. Isosceles Triangle (2 sides are equal) 3. Scalene Triangle (no sides are equal)
Based on the measure of their angles, there are 3 types of triangles: 1. Acute Triangle (all angles are less than 90º) 2. Obtuse Triangle (one angle is greater than 90º) 3. Right Triangle (one angle is 90º)
Area of a Triangle = 1/2 × Base × Height