If this is an equilateral triangle, we need half of it to find the height which is a leg of a right triangle with a hypotenuse of 15. That means that the base of this half triangle is 7.5. Use Pythagorean's Theorem to fine the height. [tex] x^{2} =(15) ^{2} -(7.5) ^{2} [/tex]. x = 12.99 or 13
