# Based Upon Sides

1. Scalene triangle
A triangle whose all sides are of a different length is a scalene triangle.

Area  where

S (semi perimeter)

Example
What is the area of the triangle with side lengths 4 units, 5 units and 10 units?
Solution
This triangle is not possible. (Since the sum of lengths of the two sides > Length of the third side)

1. Isosceles triangle
A triangle whose two sides are of an equal length is an isosceles triangle.

Height

Area
1. Equilateral triangle
A triangle whose all sides are of an equal length is called an equilateral triangle.

In any equilateral triangle, all the three sides are of an equal length, so a = b = c

Height = (side)

Area

# Based Upon Angles

1. Right-angled triangle
A triangle whose one angle is of 90Â° is called a right-angled triangle. The side opposite to the right angle is called the hypotenuse.

Area  Ã— base Ã— perpendicular
1. Obtuse-angled triangle
If one of the angles of the triangle is more than 90Â°, then the triangle is known as an Obtuse angled triangle. Obviously in this case, rest of the two angles will be less than 90Â°.
1. Acute-angled triangle
If all the angles of the triangle are less than 90Â°, then the triangle is known as acute angled triangle.
1. Isosceles right-angled triangle
A right angled triangle whose two sides containing the right angle are equal in length, is an isosceles right triÂ­angle.

In this case, Hypotenuse (h)

Perimeter = 2a + h = 2a +

= Hypotenuse