Triangle

A triangle is a plane figure with three straight sides and three angles. 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°.

Types of Triangle

Based on the angles and side length, the triangles are classified into six types.

Based on the length of the sides, the triangle is classified into:

	Scalene Triangle – All the sides of a triangle of different lengths, no equal angles and sides.
	Isosceles Triangle – Two sides of equal length and two egual angles. An isosceles triangle also has two angles of the same measure, the angles opposite to the two sides of the same length.
	Equilateral Triangle – Three sides of the same length. An equilateral triangle is also a regular polygon with all angles measuring 60°.

Based on the angles, the triangles are 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

Area and Perimeter

Area of Triangle = 0.5 x base x height

a is the length of the base of the triangle, and h is the height or altitude of the triangle.

The term «base» denotes any side, and «height» denotes the length of a perpendicular from the vertex opposite the base onto the line containing the base.