You're right! Here's an explanation:
perimeter of a rectangle = length + length + width + width
P = L + L + W + W
P = 2L + 2W
To solve this equation for L , subtract 2W from both sides.
P - 2W = 2L
Divide both sides of the equation by 2 .
(1/2)(P - 2W) = L
P/2 - W = L
L = P/2 - W This is a formula just like the quadratic formula is a formula.