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Homework Help: Differential Equations Problem

  1. Sep 13, 2006 #1
    Could someone please help me with this problem:

    Consider the differential equation d^2y/dx^2 + dy/dx - 6y = 0 with the initial conditions y(0)= 6 and y'(0)=2. Determine whether the following functions are solutions:

    a. y=4e^(2x) + 2e^(-3x)

    b. y=2e^(2x) + 4e^(-3x)

    If someone could please at least help me get started on this I would appreciate it very much

    Thanks,
    Dao Tuat
     
  2. jcsd
  3. Sep 13, 2006 #2
    You need to substitute the two solutions given into the differential equation, and see if they come to zero. I don't think they're asking you to solve it directly.
     
  4. Sep 13, 2006 #3
    Be sure to also check that the solutions satisfy the given initial conditions.
     
  5. Sep 14, 2006 #4
    So then neither a or b are solutions, right?
     
  6. Sep 14, 2006 #5
    Only a. is a solution because b. doesn't satisfy y'(0) = 2 (y'(0) = -8). They both fit the equation, though, as can seen below.

    (16e^(2x) + 18e^(-3x)) + (8e^(2x) - 6e^(2x)) - 6*(4e^(2x) + 2e^(-3x)
    (8e^(2x) + 36e^(-3x)) + (4e^(2x) - 12e^(-3x)) - 6*(2e^(2x) + 4e^(-3x))
     
    Last edited: Sep 14, 2006
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