Equilateral triangles do not have a radius. A circle circumscribed about an equilateral triangle does have a radius however. To the extent that is what you meant to say, that radius is related to the measure of the side of the triangle in the following fashion:
where is the measure of a side of the equilateral triangle and is the measure of the radius of the circumscribed circle.
I showed you in my last post how to calculate the area of an equilateral triangle using the measure of a side. Use the same method here.
