Hi,
Let x represent the third side of the right triangle with shorter sides of 3 and 4
Applying the Pythagorean Theorem
x =
Perimeter of this right trangle = 3 + 4 + 5 = 12
Question states the diagonal of the square whose area is to determined = 12
Once again, applying the Pythagorean Theorem: s being the length of each side
s^2 + s^2 = 12^2
2s^2 = 144
s^2 = 72
s = sqrt(72)
Area of a square = l*w = s*s = sqrt(72)*sqrt(72) = 72 square units