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Quick Diff. Eq. Question

  1. Dec 11, 2008 #1
    Hey all, I hope this isn't against the forum rules or anything, but I'm studying for an upcoming final and had a quick question about one of the practice questions we have. I'm not sure I understand the concepts at work here, and was hoping someone could give me some insight.

    http://img301.imageshack.us/img301/7656/40567729co1.png [Broken]

    Thanks in advance!
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Dec 12, 2008 #2
    Go through each answer and find the derivative. Then, check to see which satisfy the relationship in the question.
    Last edited by a moderator: May 3, 2017
  4. Dec 12, 2008 #3


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    Science Advisor

    Another method, it this weren't "multiple guess", is to use "variation of parameters".

    Knowing that [tex]\frac{2e^{2t}}{1+ e^{2t}} [/tex] is a solution, set
    [tex]y= u(t)\frac{2e^{2t}}{1+ e^{2t}}[/tex]
    and substitute into the equation. That will give you a separable equation for u(t). Knowing that, you can find y.
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