calculus
posted by hartati
Sam has 1200 feet of fencing and wants to fence off a rectangular field that borders a straight river. He needs no fence along the river. Express the area of the field as a function of its dimension. Find the dimensions of the field that has the largest area.

Reiny
length parallel to river  x ft
each of other two sides  y ft
2x + y = 1200 > y = 1200  2x
area = xy
= x(12002x)
= 1200x 2 x^2
since you labeled it "Calculus"
d(area)/dx = 1200  4x
= 0 for a max of area
4x = 1200
x = 300
width = 300
length = 1200  2(300) = 600
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