Is an equilateral triangle equal to an isosceles triangle?
An isosceles triangle has at least two congruent sides.
An equilateral triangle has three congruent sides.
So, an equilateral triangle is a special case of isosceles
triangles.
Since the equilateral triangle has three congruent sides, it
satisfies the conditions of isosceles triangle.
So, equilateral triangles are always isosceles triangles.
Source: www.icoachmath.com