Math
posted by Alex
A rectangular ﬁeld is to be fenced in on four sides with a fifth piece of fencing placed Parallel to one of the shorter sides, so that the ﬁeld is split in two parts. If 1600 m of fencing is available, ﬁnd the largest possible area for this enclosure. What dimensions give this maximum area?

Reiny
let the length be y m
and each of the shorter pieces (the width) be x
we know 2y + 3x = 1600
y = 800  3x/2
area = xy
= x(8003x/2)
= 800x  3x^2 /2
find the first derivative, set it equal to zero and find x
then find y, and the area xy 
scott
xmax is on the axis of symmetry of the parabola
b / 2a = 800 / (2 * 3/2) = 800 / 3
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