Pythagorean theory baby! Okay so the Pythagorean theory is a² + b² = c² so lets draw a triangle and label our sides. So we know 8² + 15² = c² so I'm going to find the square root of all of our numbers. We get 64 + 225 = c² so then add 64 + 225 = 289 then I take the square root of 289 which equals 17 . This answer also makes sense because out hypotenuse should always be bigger then the legs.