The square of the hypotenuse of a right-angled triangle is equal to the sum of the squares of the other two sides. You can use Pythagoras' Theorem to calculate QR: a^2 + b^2 = c^2 5^2 + 12^2 = QR^2 25 + 144 = QR^2 169 = QR^2 This means that the square root of 169cm is QR, which is 13cm.
