Which of the following are the sides of a right triangle?

Correct answer: 15, 20, 25. 15² + 20² = 225 + 400 = 625 = 25², so these sides satisfy the Pythagorean theorem.

Background: The longest side is the hypotenuse.

• 10, 9, 18: 9² + 10² = 181, but 18² = 324.
• 20, 18, 30: 18² + 20² = 724, but 30² = 900.
• 15, 20, 27: 15² + 20² = 625, but 27² = 729.

Did you know? 15, 20, 25 is the 3-4-5 triangle multiplied by 5.

Memory trick: 3-4-5 × 5 = 15-20-25.