Asked by Mathew

A rectangular eld is to be fenced o along the bank of a river; no fence is required along the bank
of the river. The material for the fence costs 8 dollars per running foot for the two ends and 16
dollars per running foot for the side parallel to the river. If the area of the eld is to be 12,000
sq. feet and the cost of the fence is not to exceed 3,520 dollars, what are the restrictions on the
dimensions of the eld?

I'm not sure how to solve this. help me pleasee. thank you
Answered by Reiny
What's an eld ?

let the side parallel to the rive by y ft
let the other sides be x ft each
so xy = 1200
y = 1200/x

cost of fence = 16y + 8(2x)
= 16(1200/x) + 16x
= 19200/x + 16x

d(cos)/dx = -19200/x^2 + 16
= 0 for a min cost.
16x^2 = 19200
Can you finish it?
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