Question

A farmer will enclose a rectangular region along a river. He will not fence along the river.
1. If he uses 800ft of fencing, express the length of the rectangle in terms of w, the width.
2. Express the area of the enclosed rectangle in terms of the width, w.
3. What should the width be so that the enclosed area is 80,000 sqft

Answer 1

L = (800-2w)/2 = 400-w
a = w(400-w)
w(400-w) = 80000
solve for w as usual

Answer 2

oops. I missed the part about the river.
So, assuming the length is along the river,
L = 800-2w
If the width is along the river,
L = (800-w)/2
and proceed as above