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Homework Help: Functions in differential calculus

  1. Mar 5, 2012 #1
    1. The problem statement, all variables and given/known data
    Here's the link (I scanned my homework), since it's hard to type the entire question on here, considering the mathematics-related symbols. I just want to make sure you all understand what I am asking.

    http://i1056.photobucket.com/albums/...ash5dash55.png [Broken]

    2. Relevant equations
    f(x,y)= 3x^2 + 7y^2

    3. The attempt at a solution
    What I did was derive the function f(x,y)= 3x^2 + 7y^2, which resulted in the answer E_1= 6 delta x, E_2= 14 delta y. However, the answer was declared wrong. I do not know what I did wrong. Was I supposed to derive the function? Could you please help explain this to me? Could you give me an example related to this problem? Please do what you are allowed to do to help me. I understand the need to figure things out for myself.

    Thank you so much!
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Mar 5, 2012 #2

    Ray Vickson

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    Science Advisor
    Homework Helper

    Your link returns "file not found".

    Last edited by a moderator: May 5, 2017
  4. Mar 5, 2012 #3
    Here is the link. http://i1056.photobucket.com/albums/t377/swimmergrl85/Mathematics/cal3dash5dash55.png [Broken]

    I don't know how the link got screwed up before.

    I figured it out. It was obvious after I did 3 delta x^2 + 7 delta y^2, E_1= delta x and E_2= delta y. I divided the 3 delta x^2 +7 delta y^2 by the E_1 and E_2 values, and got 3 delta x for E_1, and 7 delta y for E_2. I use a homework program where I submit my answer, and it tells me if I am right or not, and I was right. I need to believe in myself more.

    Thanks for your reply though.
    Last edited by a moderator: May 5, 2017
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