How do you find the perimeter without knowing the length of each side?

Answer 1

For rectangles, there are only two side lengths and the perimeter is obviously

P = 2 (L + W). For squares, P = 4S.

If you know the diagonal length of a rectangle, you only need one side to find the other side length using the Pythagorean theorem (d squared = side a squared + side b squared).

If it is a square, knowing the diagonal gives you the perimeter: it is 4 times the square root of (d squared divided by 2).

In other more complex figures you will need to use more concepts like parallel lines, perpendicular lines, and other geometric theorems like the Pythagorean theorem.