calculus
posted by help please. on .
An open rectangular box having a volume of 256 is to be constructed from a tin sheet.
Find the dimensions of such a box if the amount of material used in its construction is to be minimal.
Hint: Let the dimensions of the box be x by y by z . Then, xyz=256 and the amount of material used is given by . Show that f(x,y)= xy + 512/x + 512/y
minimize f(x,y)

we know xyz = 256
so z = 256/(xy)
Surface area = SA
= 2xy + 2xz + 2yz
= 2xy = 2x(256/(xy)) + 2y(256/(xy))
= 2xy + 512/y + 512/x
hope that helps. 
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