A farmer is constructing a rectangular pen with one addtional fence across its width.find the maximum area that can be enclosed with 2400m of fencing .

Answer 1

3x+2y = 2400
a = xy = x(2400-3x)/2
= 1200x - 3/2 x^2
this is a parabola, with vertex at (400,240000)

as usual, note that the fencing is evenly divided between widths and lengths.