A box with a square base and no top is to be built with a volume of

6912 in^3. Find the dimensions of the box that requires the least amount of material. How much material is required at the minimum?

1 answer

Surface area: 2Lh+2Wh+LW
volume=Lhw or h= 6912/Lw

surface area=2L(6912)/Lw+2w*6912/Lw + Lw

= 2*6912/w+2*6912/L+Lw
now, it has a square base (I just saw that, so L=W)
=2*6912/x+2*6912/x+x^2

take the derivative of area /dx
set to zero.
0=-4*6912/x^2+2x

or x^3=8(6912)
L=W=38.0976 inch
solve for h now h=6912/Lw