You can 
put this solution on YOUR website!   
Hi
Area of square = s^2, where s is the length of each side
  s^2 = 484
   s = 22cm  (tossing out negative solution for length)
Applying the Pythagorean Theorem
 (22cm)^2 + (22cm)^2 = d^2
     968cm^2 = d^2
   d = 31.1127cm