SOLUTION: If a company makes a block of cheese designed to have the height exactly five times the width and the ideal of 1800mm^3 using the least possible surface area, what would be the len

Algebra ->  Volume -> SOLUTION: If a company makes a block of cheese designed to have the height exactly five times the width and the ideal of 1800mm^3 using the least possible surface area, what would be the len      Log On


   



Question 1010811: If a company makes a block of cheese designed to have the height exactly five times the width and the ideal of 1800mm^3 using the least possible surface area, what would be the length
Answer by josgarithmetic(39630) About Me  (Show Source):
You can put this solution on YOUR website!
Most of the way through, but short of complete finish:

y, height
x, length
z, width

The description gives from these chosen variables,
system%28y=5z%2Cxyz=1800%29
and the area function you want, depending on name you choose,
A=2xy%2B2yz%2B2xz.

Substitutions to put A as a function of just one single variable...
x%285z%29z=1800
5xz%5E2=1800
but z is width, and the question asks for LENGTH to minimize area.
Try again...
-
z=y%2F5
Use in the volume,
xy%28y%2F5%29=1800
still giving a square for what we want to substitute.
-
Try first aiming for one of the other variables for the single variable in A.
Go back to description, and substitute for y in A.
A=2x%285z%29%2B2%2A5zz%2B2xz
A=10xz%2B10z%5E2%2B2xz
A=12xz%2Bz%5E2-------want to eliminate, subst for x or z...

Look again at description.
x%285z%29z=1800
5xz%5E2=1800
x=1800%2F%285z%5E2%29=360%2Fz%5E2------Substitute for x in A.

A=12%28360%2Fz%5E2%29z%2Bz%5E2
highlight%28A=4320%2Fz%2Bz%5E2%29-------Variable z must be used, take derivative, and find what makes A the minimum, and then find the corresponding x value, the asked for length.

---------
continuing,

A=4320%2Fz%2Bz%5E2

dA%2Fdz=2z-4320%2Fz%5E2 You fill in the steps to that.

Set deriv to 0.
2z%28z%5E2%29%2Fz%5E2-4320%2Fz%5E2=0
%282z%5E3-4320%29%2Fz%5E2=0
The denominator does not take meaning here ...
2z%5E3-4320=0
z%5E3-2160=0
z%5E3=2160
and you can fill-in the steps...
highlight%28z=6sqrt%2810%29%29

Again use the equations from the description to reach the corresponding value for x, the length.