A square courtyard has diagonals paths that are each 42 meters long. What is the perimeter of the courtyard?

First you need to determine the length of each side, based on knowing the diagonal (see the Related Question below). 42 / 1.4142 = 29.69876922...

Once you know the length of a side, the Perimeter of the square would be 4L. So 29.69876922 x 4 = 118.795