Question

A metal Wire 72 m long is bent from a rectangle. Find its dimensions, when its area is maximum

Answer 1

if rectangle's 2(l+b) =72/2

l+b = 36/2

l = 18 - b

b = 18 - l

so, area of the rectangle is

= l × b

= 18 - b × 18 -l

= 18^2 -18l - 18b +lb

= 324 -18(l+b) +lb