 # Triangle Definition

In Geometry, the shapes are generally classified as 2D shapes and 3D shapes. The shapes with two measures such as length and height are called two-dimensional shapes, whereas the shapes with three measures such as length, height and width are called three-dimensional shapes. In this article, let us discuss in detail the definition, types and properties of one of the two-dimensional shapes called “Triangle”.

## Triangle Definition in Maths

A triangle is a polygon with three sides having three vertices. The angle formed inside the triangle is equal to 180 degrees. It means that the sum of the interior angles of a triangle is equal to 180°. It is a polygon having the least number of sides. In other words, a triangle is defined as a three-sided two-dimensional figure whose interior angles are equal to 180°.

## Types of Triangle

Based on the angles and side length, the triangles are majorly classified into six types. Let us discuss in detail about the six types of triangles. Based on the length of the sides, the triangle is classified into:

• Scalene Triangle – All the sides of a triangle having different side measurement
• Isosceles Triangle – Two sides of a triangle are of the same measure
• Equilateral Triangle – All the three sides of a triangle having equal side measurements

Based on the angles, the triangles are further classified as:

• Acute Angle Triangle – All the angles of a triangle are less than 90 degrees
• Obtuse Angle Triangle – One of the angles of a triangle is greater than 90 degrees
• Right Angle Triangle – One of the angles of a triangle is equal to 90 degrees

## Triangle Formula

If “b” be the base and “h” be the height of a triangle, then the formula to find the area of a triangle is given by

Area of triangle, A = (½) bh square units

If “a”, “b”, “c” are the sides of a triangle, the perimeter of a triangle is given as

Perimeter of a triangle, p = a + b + c units

### Triangle Properties

The important properties of the triangle are

• The sum of the interior angles of a triangle is 180 degrees
• When two sides of a triangle are added, it is always greater than the third side
• Similarly, if the two sides of a triangle are subtracted, it is always less than the third side
• Two triangles are said to be similar if the corresponding angles are congruent and the corresponding side lengths are proportional.

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Quiz on Triangle Definition