Question

Given the area of a rectangle is A = LW. If three sides of the rectangle are fixed, I.e. 2W + L = 40, find L and W such that you maximize the area of the rectangle.

Is it L=10, W=20?

Answer 1

I meant W=10, L=20

Answer 2

2 W + L = 40
so
L = 40 - 2 W

A = W L = W (40 - 2 W) = 40 W - 2 W^2
dA/dW = 40 - 4 W
W = 10
so yes