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)      (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, 
  
and the area function you want, depending on name you choose,  
 .
 
 
Substitutions to put A as a function of just one single variable... 
  
  
but z is width, and the question asks for LENGTH to minimize area. 
Try again... 
- 
  
Use in the volume, 
  
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. 
  
  
 -------want to eliminate, subst for x or z...
 
 
Look again at description. 
  
  
 ------Substitute for x in A.
 
 
  
 -------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,
 
 
 
 
 
   You fill in the steps to that.
 
 
Set deriv to 0. 
  
  
The denominator does not take meaning here ... 
  
  
  
and you can fill-in the steps... 
 
 
 
Again use the equations from the description to reach the corresponding value for x, the length. 
 
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