The square has a diagonal of 26yd. The same diagonal is the hypotenuse of the right triangle whose legs are s, the side of the square.
Using the Pythagorean theorem:
26² = s²+s²
26²= 2s²
676=2s²
s²= 338
The area of a square whose side is s, is s².
s²=338 yd
Hence:
The area of the square is 338 yd².
