If a field is to be fenced on three sides, what is the maximum area if there are 20m of fencing available?
2 L + W = 20 ... W = 20 - 2 L
a = L * W ... substituting ... a = L (20 - 2 L) = 20 L - 2 L^2
the maximum is on the axis of symmetry of the parabola (graph)
Lmax = -20 / (2 * -2) = 5
substitute back to find Wmax , then calculate maximum area