The side length of the square is 2*((8/2)^.5) = 4cm
The area is 4^2 = 16 cm
See the attached picture. The parts labeled a and b are both the same length since this is a square. And each of them is half of the side length of the square. We can find the length of a and b using the Pythagorean theorem because the 8cm is a hypotenuse of a right triangle. So we find a, and multiply by 2 to get the square side length. Then we square that to get the square area.
