What is a Triangle?
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.
Properties of a Triangle
 A triangle has three sides, three vertices, and three angles.
 The sum of the three interior angles of a triangle is always 180°.
 The sum of the length of two sides of a triangle is always greater than the length of the third side.
 A triangle with vertices P, Q, and R is denoted as △PQR.
Different Types of Triangles
To classify triangles according to their angles, we measure each of its interior angles. Triangles can be classified by angles, as:



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. Some of the triangles classified on the basis of both angles and sides are:



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