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The manufacturer wants to triple the volume of the rectangular prism (7*9*4 - length*width*height). Which dimensions should he triple to use the least amount of material? Please explain your reasoning with work provided. Thank You!


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Guest May 9, 2017
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V = l*w*h

A = 2*l*w*h*(1/l + 1/w + 1/h)

 

Suppose the dimension l is tripled, then the new prism has an amount of material

Al = 6*l*w*h*(1/3l + 1/w + 1/h) = 6*l*w*h*(1/l + 1/w + 1/h - 2/3l) = 3A - 4wh

 

Similarly for the dimensions w and h, Aw = 3A - 4lh and Ah = 3A - 4lw.

 

To have the least amount of material for the prism, choose Max(wh, lh, lw) = lw

which implies the dimension h is tripled with the prism having a volume of 7*9*12.

Guest May 9, 2017
edited by Guest  May 9, 2017

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