1. Not finding help here? Sign up for a free 30min 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!

Solve a differential equation

  1. Mar 5, 2015 #1
    1. The problem statement, all variables and given/known data
    dy/dx=2xcos(y)-xy^3



    2. Relevant equations


    3. The attempt at a solution
    dy/dx=2xcos(y)-xy^3=x(2cosy-y^3)
    dy/(2cosy-y^3)=xdx


    I can not integrate the left side of the equation. Can someone help me please?
     
    Last edited: Mar 5, 2015
  2. jcsd
  3. Mar 5, 2015 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Hello MarkZone. Welcome to PF.

    Show us what you have tried, that's a requirement here.

    As a small hint: Try to factor your expression.
     
  4. Mar 6, 2015 #3

    Mark44

    Staff: Mentor

    @SammyS, after an edit, the OP now has separated the DE into
    $$\frac{dy}{2\cos(y) - y^3} = xdx$$
    I don't see how factoring sheds any light here. Maybe I'm missing something.
     
  5. Mar 6, 2015 #4

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    That is separated. Right?

    That was the original question.

    ... That is a difficult integral for sure.
     
  6. Mar 6, 2015 #5

    Mark44

    Staff: Mentor

    From the thread title, the goal is to solve the DE, but in the original (unedited) post, the OP said he was not able to separate the DE. I agree that the DE is now separated, but my question pertained to how to solve the DE.
     
  7. Mar 6, 2015 #6

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Right. I agree.

    I also don't see how the separation helps, unless we want a numerical solution.
     
  8. Mar 6, 2015 #7
    Thanks everyone
     
  9. Mar 6, 2015 #8

    LCKurtz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    @MarkZone: Can you give us the context where this DE came from?
     
  10. Mar 6, 2015 #9
    Oh It was jist from my math hw. There is no context for this.
     
  11. Mar 7, 2015 #10

    LCKurtz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Of course there is context. What topics were you covering in your text in the section where this problem was given? What approaches were you expected to try?
     
  12. Mar 7, 2015 #11
    It is a AP calculus problem on the topic "Differential Equations & Slope fields." The original question asks me to solve this by the separation of variables method. That is all I know and my teacher does not know how to solve this either.
     
  13. Mar 7, 2015 #12

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    The method of slope fields gives you a way to sketch the solutions. You don't necessarily actually find an analytic solution.

    Google "slope field method" .
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Solve a differential equation
Loading...