1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Optimization: Open Box help

  1. Nov 22, 2009 #1
    1. The problem statement, all variables and given/known data
    http://img7.imageshack.us/img7/1826/43544187.jpg [Broken]


    2. Relevant equations



    3. The attempt at a solution
    whats wrong with my answers? everything looks right to me... :S
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Nov 23, 2009 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    The only thing wrong that I see is that you haven't answered the question. You said that the volume will be minimized. You have given x, but you haven't found y and have not said what the dimensions are.
     
  4. Nov 24, 2009 #3
    y=2500/17.12

    the thing is, i only have to choose the right answer from those drop down menu boxes..
    so i must of chosen something wrong.. but what? i dont see any mistakes
     
  5. Nov 24, 2009 #4
    okay my derivatives look fine.. when f'(x)=0 x=17.1
    f''(x) > 0 for x>0.. thats right because if plugging in a negative number i will get f''(x) = -..

    so whats wrong?
     
  6. Nov 24, 2009 #5
    can someone please help me?
     
  7. Nov 25, 2009 #6
    why are u guys ignoring this post? is it something that i said?
    for the last part where it says it will be relative min, when x=___
    would it be -21.5446 ?
    i got it by getting the second derivative equal to 0
     
  8. Nov 25, 2009 #7

    Mark44

    Staff: Mentor

    One of your entry boxes says "This implies that the surface area is given in S only..."
    Except for this, everything else it looks fine.

    Here's a tip you might consider. Many or most of the problems you have posted have oddball numbers such as a volume of V = 2500.1055 cm^3.
    I did all of my calculations using V, and replaced V only in the very last step. This saved my from writing 2500.1055 a bunch of times.

    For example, A = x^2 + 4V/x. It's easy to get dA/dx = 2x -4V/x^2. Rewriting this as dA/dx = 2x -4Vx-2, it's easy to get the second derivative and verify that it's positive for all x > 0.
     
  9. Nov 25, 2009 #8


    i did it this way.. i substituted V only at the very end and i got the same answers..
    and about the "This implies that the surface area is given in S only..." yeah i didnt read it carefully but still. now i got it tnx!
     
    Last edited: Nov 25, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Optimization: Open Box help
Loading...