What two perfect squares add up to 400?

Question

I'm trying to do pythagorean theorem having a² + b² = 20². It has to be two different numbers. 

Answer 1

One Pythagorean triple (numbers that make the equation true) is 3, 4, 5.

Any multiple of these numbers also are Pythagorean triples, e.g., 6, 8, 10

In this case the triple is 12, 18, 20.