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# Triangle

A polygon is a two dimensional shape enclosing an area. A shape must require at least three sides to enclose something and the shape which has three sides is called a triangle.
Each point of intersection of a set of two sides is called as vertex.Thus, a triangle is the first member in the family of polygon.
The name is derived from Greek in which the prefix ‘tri’ refers to the number 3.
A triangle has a number of special properties and let us look into some of those. Before that we shall discuss about different types of triangles.

 Related Calculators Area of Triangle Triangle Calculator Area of a Equilateral Triangle Calculator Area of a Right Triangle Calculator

## Types of Triangles

Triangles are classified into different types on the bases of different considerations.

Based on the number of sides and interior angles, triangles are classified as equilateral, isosceles and scalene.
• In an equilateral triangle, all sides are congruent and as per geometrical theory all the internal angles are also congruent. In an equilateral triangle, the measure of each interior angle is $60^{\circ}$ irrespective of the size of the triangle.
• An isosceles triangle has two congruent sides and accordingly the corresponding angles are also congruent.
• In a scalene triangle, neither any set of sides nor any set of the interior angles are congruent.

Triangles are also classified on the types of interior angles.
• If all the interior angles of a triangle are acute (measuring < 90o), then it is termed as an acute triangle.
• A triangle is called obtuse triangle if any of the (it can be only one) internal angles is obtuse (measuring > 90o).
• If one of the interior angles of a triangle is a right angle (measuring exactly 90o), the triangle is named as right angle triangle or simple as right triangle.

## Properties of Triangles

• In any triangle, the sum of the measures of all interior angles is $180^{\circ}$. This is the reason that each internal angle in an equilateral triangle measures exactly $60^{\circ}$.
• The area of any triangle is given by the unique formula as  A = $\frac{1}{2}$ $\times$ b $\times$ h, where ‘b’ is the measure of the base (any of the three sides can be considered as base) and ‘h’ is the measure of the altitude drawn on the same base from the opposite vertex. There are several other formulas which are used depending upon the available information.