Let's say the short leg measures x inches. Then the long leg must measure 2x inches, and the hypotenuse of the triangle is 21 inches, or the width of the solar panel. Using Pythagoras:and recognizing that a = x, b = 2x, and c = 21 we can write: Lastly, rationalize the denominator: Which gives us an expression for the short side. The long side is twice that, so Long side = I'll leave the calculator work to you.