An equilateral triangle is a special case of isosceles triangles, in which all three sides of the triangle are equal:
Since it is a special case of isosceles triangles, all the properties of isosceles triangles apply to an equilateral triangle as well, so the base angles are equal.
But since in this case, the third side is also the same, any side can serve as the base, and so we see that all angles must be the same.
And since the sum of all angles is 180°, each angle of an equilateral triangle must be 180°/3=60°.
Now that we've explained the basic concept of equilateral triangles in geometry, let's scroll down to work on specific geometry problems relating to this topic.