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!

Can someone help me with my differential equation?

  1. Sep 8, 2014 #1
    1. The problem statement, all variables and given/known data

    I want to solve number 13. I have my work on the attached file.

    2. Relevant equations



    3. The attempt at a solution

    I've tried to solve the system by elimination and substitution. I keep failing again and again
     

    Attached Files:

  2. jcsd
  3. Sep 9, 2014 #2

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Great! What's number 13? Your attachment (which is upside down, thank you very much) has several different scribbles at the top of the page, one of which appears to be '11.'

    The thread title mentions 'differential equation', but your thread talks about 'elimination and substitution', which doesn't suggest solving a DE.

    Care to start over?
     
  4. Sep 9, 2014 #3

    Mark44

    Staff: Mentor

    Please take the time to post your work right side up. Better yet, type your work here in the input pane as text.
     
  5. Sep 9, 2014 #4

    Mark44

    Staff: Mentor

    Please take the time to post your work right side up. If you can't be bothered to make it easy to help you, many homework helpers here will choose not to jump in.

    Better yet, type your work here in the input pane as text.
     
  6. Sep 9, 2014 #5
    I apologize, I posted this in haste and did not check to see if my post was upside down. I do not see how it's illegible. You will see towards the right there is a #13. The problem has two equations that are boxed in with C1 and C2. I need to solve for the two variables. I can't seem to get the correct values of C1 and C2.

    y = C1e^x + C2e^x
    y' = C1e^x - C2e^-x

    y(-1) = 5
    y'(-1) = -5

    In case it's not legible.

    I end up with a systems of equations after I plug in the info I am given. Which I have boxed in on the attachment.
     
  7. Sep 9, 2014 #6
    The attachment
     

    Attached Files:

  8. Sep 9, 2014 #7

    Mark44

    Staff: Mentor

    Typo in the first equation above. It should be y = C1e^x + C2e^(-x)

     
  9. Sep 9, 2014 #8

    Mark44

    Staff: Mentor

    You are substituting incorrectly.
    y(-1) = 5 means you should replace x by -1 and y by 5. You are doing the opposite.
    Same thing in the 2nd equation.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted