How to find the length of a square given the perimeter?

If you have the perimeter of a square, the outside is made of four equal sides.

After that I would draw in the diagonal and see that it forms a right triangle, you can also notice that it forms a 45 45 90 right triangle. From there, you can either use the Pythagorean theorem, take cos(45 degrees), or remember the relationship between the sides for a 45 45 90 triangle.

Three options.