SOLUTION: A box with a square bottom and no top must contain 108 cubic inches. What dimensions will minimize the surface area?

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Question 205397This question is from textbook Caluculus sucess in 20 minutes a day
: A box with a square bottom and no top must contain 108 cubic inches. What dimensions will minimize the surface area? This question is from textbook Caluculus sucess in 20 minutes a day

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A box with a square bottom and no top must contain 108 cubic inches. What dimensions will minimize the surface area?
:
Let x = length and width of the bottom of the box
then
108%2Fx%5E2 = the height of the box
;
Surface area with no top = (L*W) + 2(L*H) + 2(W*H)
:
SA = x^2 + 2(x*108%2Fx%5E2) + 2(x*108%2Fx%5E2)
Cancel x
SA = x^2 + 2(108%2Fx) + 2(108%2Fx)
:
SA = x^2 + (216%2Fx) + (216%2Fx)
:
SA = x^2 + (432%2Fx)
Graph this equation to find the min surface area for the given volume
Surface area is the y axis.
+graph%28+300%2C+200%2C+-4%2C+10%2C+-30%2C+150%2C+x%5E2%2B%28432%2Fx%29%29+
:
Minimum: x = 6" is the length and the width of the bottom
:
Find the Height
h = 108%2F6%5E2 = 3" is the height
:
check the volume
6 * 6 * 3 = 108 cu/in
;
:
Interesting that the min surface area is also 108 (but sq/in)
(6*6) + 2(6*3) + 2(6*3) = 108