How to solve #2 if you don’t know any of the side lengths?? (We’re learning about Pythagorean Theorem)

Answer:
Applying Pythagorean theorem in right triangle with c is longest side and a, b are the other sides:
=> c^2 = a^2 + b^2
=> a^2 = c^2 - b^2
=> b^2 = c^2 - a^2
Hope this helps!
:)