Inscribed equilateral triangle:
Draw apothem from center perpendicular to a side.
Draw radius from center to vertex of same side.
Triangle formed is 30-60-90.
If hypotenuse(radius) is 8, then side opposite the 30 deg. angle is 4 (apothem).
Side opposite 60 degree angle is
Thus, the length of a side is
, where P=perimeter, a=apothem