# Definition:Triangle (Geometry)/Equilateral

## Definition

An equilateral triangle is a triangle in which all three sides are the same length:

That is, a regular polygon with $3$ sides.

Thus it can be seen that an equilateral triangle can be considered to be a special case of an isosceles triangle.

## Euclid's Definition

In the words of Euclid:

Of trilateral figures, an equilateral triangle is that which has its three sides equal, an isosceles triangle that which has two of its sides alone equal, and a scalene triangle that which has its three sides unequal.