Height of an equilateral triangle, h = a\(\frac{\sqrt{3}}{2}\), where a is the side of the equilateral triangle. 10\(\sqrt{3}\) = a\(\frac{\sqrt{3}}{2}\) cross multiply--> 2 x 10\(\sqrt{3}\) = a\(\sqrt{3}\) \(\sqrt{3}\) cancels out \(\sqrt{3}\) on both sides 20 = a The perimeter of an equilateral triangle is: P = 3a P = 3 * 20 = 60cm