What is the length of the diagonal of a 10 by 10 ft square?

To find the length of the diagonal of a square, we can use the Pythagorean theorem. In a square, the diagonal divides the square into two right-angled triangles. The Pythagorean theorem states that the square of the length of the diagonal is equal to the sum of the squares of the two sides. Therefore, for a 10 by 10 ft square, the length of the diagonal would be the square root of (10^2 + 10^2) which is √(100 + 100) = √200 = 10√2 feet.