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!

Homework Help: Help me to explain this

  1. Nov 5, 2009 #1
    1. The problem statement, all variables and given/known data

    I have my notes below, however I don't understand the part where it says that:

    xp(t) = A, where did this come from?

    http://img142.imageshack.us/img142/4733/questionub.th.jpg [Broken]

    2. Relevant equations

    3. The attempt at a solution
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Nov 5, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi -EquinoX-! :smile:

    You have x'' -6x' + 5x = 5.

    The general solution is the characteristic solution plus any particular solution.

    For the particular solution, you make an intelligent guess …

    in this case, it seems obvious that a constant will do (in fact, I don't know why he bothered to say let xp(t) = A, and solve for A … I'd just have gone straight to xp(t) = 1)

    (but if there was a 5x on the RHS, you'd choose a linear function, if there was an e7x, a multiple of e7x, and so on)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook