Types of Triangles

An isosceles triangle has two edges of the same length.

Two of its vertex angles must also be the same size.

It has one line of symmetry.

Isosceles triangles are often found in circles:

An equilateral triangle has all three edges the same length.

All of its vertex angles are the same size: \[ 60^\circ \]

It has three lines of symmetry.

A scalene triangle has all its edges of different lengths.

All of its vertex angles are different sizes.

It has no symmetry.

An acute triangle has no vertex angle greater than \[ 90^\circ. \]

It may be isosceles or scalene.

An obtuse triangle has one vertex angle greater than \[ 90^\circ. \]

It may be isosceles or scalene.

A right‑angled triangle has one vertex angle equal to \[ 90^\circ. \]

It may be isosceles or scalene.