You need to construct a closed rectangular box with the volu
You need to construct a closed rectangular box with the volume 60 m^3. The material used for the sides will cost $1/m^2, while the material for the bottom will be $3/m^2 and for the top will be $2/m^2. What dimensions will minimize the total cost of the box?
Solution
if the box dimensions are lxbxh
=> lbh = 60
and Total Cost = 3lb+2lb+1x(2lb+2bh) = 5lb+2lh+2bh
since AM is always greater than GM
=> (5lb+2lh+2bh)/3 >= (20(lbh)2)1/3
and to minimize it
5lb = 2lh = 2bh => 2.5l = 2.5b = h
=> 2.5l3 = 60
=> l = 2.8845m => h = 7.21m
So the dimensions are 2.8845 x 2.8845 x 7.21 m
