Types Of Triangles

There are different types of triangles with respect to their lengths of sides or with respect to their interior angles. To recall, a triangle is a specific type of polygon having only three sides and three angles. As the name suggests, a “tri-angle” is a type of polygon having three angles. The sum of all interior angles of a triangle will always add up to 180 degrees.

All Types of Triangles

Triangles can be broadly classified into two types, which are:

  • Triangles based on the lengths of their sides
  • Triangles based on their interior angles

These two triangle types are explained here along with their further classifications.

Types of Triangles Based on Sides and Angles:

Based on Their Sides Based on Their Angles
Equilateral Triangle Right Triangle
Isosceles Triangle Acute Triangles
Scalene Triangle Obtuse Triangles

Types of Triangles Video


Triangles Types Based on their Sides

According to the lengths of their sides, triangles can be classified into three types which are:

  • Equilateral Triangle
  • Isosceles Triangle
  • Scalene Triangle

Equilateral Triangle:

In an equilateral triangle, all the lengths of the sides are equal. In such a case, each of the interior angles will have a measure of 60 degrees. Since the angles of an equilateral triangle are same, it is also known as an equiangular triangle.The figure given below illustrates an equilateral triangle.

Equilateral Triangle

Triangle Types Fig. 1: Equilateral Triangle

Isosceles Triangle

In an isosceles triangle, the lengths of two of the three sides are equal. So, the angles opposite the equal sides are equal to each other. In other words, an isosceles triangle has two equal sides and two equal angles.  The figure given below illustrates an isosceles triangle.

Isosceles Triangle

Triangle Types Fig. 2: Isosceles Triangle

Scalene Triangle

A scalene triangle has all side lengths of different measures. No side will be equal in length to any of the other sides in such a triangle. In a scalene triangle, all the interior angles are also different. The figure given below illustrates a scalene triangle. You can see how none of the sides are equal in length.

Triangle Types Fig. 3: Scalene Triangle

Triangles Types Based on Their Interior Angles

Triangles can be classified into three types with respect to their interior angles which are:

  • Right Triangle (Or Right Angled Triangle)
  • Acute Triangle (Or Acute Angled Triangle)
  • Obtuse Triangle (Or Obtuse Angled Triangle)

Right Triangle

A right triangle is a triangle in which one of the angles is 90 degrees. In a right angled triangle, the side opposite to the right angle (90-degree angle) will be the longest side and is called the hypotenuse. You may come across triangle types with combined names like right isosceles triangle and such, but this only implies that the triangle has two equal sides with one of the interior angles being 90 degrees. The figure given below illustrates a right triangle.

Right Triangle

Triangle Types Fig. 4: Right Triangle

Acute Triangles

An acute triangle is a triangle whose has all the three interior angles are acute. In other words, if all interior angles are less than 90 degrees, then it is an acute angled triangle. The figure given below illustrates an acute triangle.

Acute Angle

Triangle Types Fig. 5: Acute Angle

Obtuse Triangles

Obtuse triangles are those in which one of the three interior angles has a measure greater than 90 degrees. In other words, if one of the angles in a triangle is an obtuse angle, then the triangle is called an obtuse angled triangle or an obtuse angled triangle. The figure given below illustrates an obtuse triangle.

Obtuse Triangles

Triangle Types Fig. 6: Obtuse Triangles

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Practise This Question

Statement 1: Area of a rectangle with length ‘l’ and breadth ‘b’ is equal to l×b.

Statement 2: All squares are rectangles with l=b

Pick the correct option from the following