The hypotenuse of a right triangle with legs 9 cm and 12 cm is

1. Apply a^2 + b^2 = c^2 with a = 9, b = 12. 2. c^2 = 81 + 144 = 225. 3. c = sqrt(225) = 15. 4. So the hypotenuse is 15 cm. _Source: Selina Concise Mathematics Class 9, Ch on Pythagoras Theorem (Mistral OCR'd PDF), section on numerical example_