In a right triangle the squares of the two legs add to the square of the hypotenuse. That relationship lets you recover any missing side from the other two when the triangle is right-angled.

Steps

1. Identify the legs a, b and the hypotenuse c (opposite the right angle).
2. Use a² + b² = c²; rearrange for the unknown side.
3. Take a square root; these drills use perfect squares.