To find the measure of an unknown side of a triangle, use a^2+b^2=c^2. (Read as "a squared plus b squared equals c squared.") The diagonal of a triangle is c. So filling in the formula you get: 8^2 + 15^2 = c^2 8^2 = 64 15^2 = 225 64 + 225 = 289 So that means c^2 = 289. To find c, find the square root of 289. √289 = 17 So c = 17, which means the measure of the unknown side is 17 m. The filled in formula: 8^2 + 15^2 = 17^2
