Triangle is a polygon with three sides. There are six special types of triangles which are classified based on their sides and angles. This page will discuss the six types of triangles based on their sides and angles.

Types of triangles

Triangles are special polygons that can be classified based on their sides and angles. The six types of triangles are scalene triangle, isosceles triangle, equilateral triangle, obtuse triangle, acute triangle, and right angle triangle.

Classification of triangle

There are two ways of classifying triangles which include:

• Classification by sides

• Classification by angles

Classification by sides

Some triangles are classified based on their sides. Below are the triangles that are classified based on their sides.

• Scalene triangle

• Isosceles triangle

• Equilateral triangle

Classification by angles

Below are the triangles that are classified based on their angles.

• Acute triangle

• Obtuse triangle

• Right triangle

**Isosceles triangle**: a triangle whose two sides are equal. In an Isosceles triangle, there is only one line of symmetry. The line of symmetry bisects the baseline at a right angle. The line of symmetry also bisects the apex of the triangle. Two base angles of an isosceles triangle are equal.

**Equilateral triangle**: a triangle that has all three sides equal. Each angle in an equilateral triangle is 60°. There are three lines of symmetry. This line of symmetry bisects the angles of the equilateral triangle and also bisects the sides of the triangle at right angles.

**Scalene triangle**: a triangle whose sides are not equal. There is no line of symmetry in a scalene triangle. None of the angles in a scalene triangle are equal.

**Right angle triangle**: a triangle that has one interior angle being 90°. In a right-angle triangle, two of the sides are perpendicular to each other.

**Obtuse triangle**: a triangle which has one interior angle being an obtuse angle and the remaining two interior angles being acute angle. An angle that is greater than 90° but less than 180°. In Euclidean geometry, the sum of the interior angles of a triangle adds up to 180° hence no two angles in the obtuse triangle can be an Obtuse angle.

**Acute triangle**: a triangle that has all three interior angles being acute angles. The angle that is measured between 0° and 90° is acute. An acute triangle is a type of triangle whose all three interior angles are acute. An acute triangle has three sides.