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Homework Help: Is this possible?

  1. Jan 3, 2007 #1
    1. The problem statement, all variables and given/known data
    If y'=0 and y=1 when x=2, and y''-4=0, find the function.

    2. Relevant equations

    3. The attempt at a solution

    I hate posting this because I am pretty sure the solution is easy but I just can't seem to see through this question...

    If y'=0 then there must be no x term in the function f(x)... thus y=C is the only possibility. So then y=1 is the only possibility for the initial conditions given.... And if y''=4 then shouldn't y'=4x+C? :/
  2. jcsd
  3. Jan 3, 2007 #2


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    Homework Helper

    The boundary values are y(2) = 1 and..? What do you mean by y' = 0? For which x is this true?
  4. Jan 3, 2007 #3
    Have you tried solving the equation y" - 4 =0, and then applying the initial conditions?

    Remember, they are not the general expression as a function of x; those are values of the function and its derivative at the point x = 2.
  5. Jan 3, 2007 #4


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    Staff Emeritus
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    These intial conditions are y'(2)=0 and y(2)=1. You have assumed y'=0 for all x.
  6. Jan 3, 2007 #5
    Ahhh okay I was misreading the damned question, :redface:... I kinda thought it was worded funny... Trying to breeze through my homework too fast I guess.

    Sorry! Thanks all, I get it now :-)
  7. Jan 3, 2007 #6


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    Science Advisor

    It didn't occur to you that is y'= 0 for all x, then y" couldn't be 4!:rolleyes:
  8. Jan 3, 2007 #7
    Yes I knew it was impossible as well. But I figured that the question was not written wrong, I should have reread the question more carefully but I was in too much of a hurry(was due in like 10 minutes). My appologies.
    Last edited: Jan 3, 2007
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