The diagonal of a rectangle 5 cm by 12 cm is

1. The diagonal forms a right triangle with the two sides. 2. d^2 = 5^2 + 12^2 = 25 + 144 = 169. 3. d = sqrt(169) = 13. 4. So the diagonal is 13 cm. _Source: Selina Concise Mathematics Class 9, Ch on Pythagoras Theorem (Mistral OCR'd PDF), section on application_