We can use the Pythagorean theorem to find the length of the third sides.
c²=a²+b²
Where c is the longest (unkwon ) side, a and b are the remaining sides. So,
c²=7²+3²
= 49+9
= 58
So, c=√58
So, the length of the third side or the side length of square is √58.
So, the area of the shaded region (square)= c²
=(√58)²
=58
So, the area of the square is 58 units².
