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ODE's on the TI-89

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  1. Aug 3, 2013 #1
    1. Is it possible for the TI-89 to solve Exact Equations?

    Ex: (2x-1)dx + (3y+7)dy = 0

    I've tried various forms of input, but I cannot find a way for the Calculator to give me a complete answer. My best luck so far was:

    (2x-1)x' + (3y+7)y' = 0. The y' part was correct, the x' part was incomplete.

    2. I've been reading about how to convert higher order equations into a form that the calculator can solve.

    Ex: y''' + 3y'' + 2y' - 5y = sin(2t)

    Can be written as:

    y'(subscript 3) = 5y(subscript 1) - 2y(subscript 2) -3y(subscript 3) + sin(2t)

    How might I enter this into the TI-89?

    3. Why does the TI-89 put tan and cot in terms of sin and cos? I have seen rather simple equations turn into complicated messes because of this.

    Thanks in advance.:smile:
     
    Last edited: Aug 3, 2013
  2. jcsd
  3. Aug 3, 2013 #2

    mfb

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    Did you try (2x-1) + (3y+7)y' = 0?

    ##y'_3##? Looks like an unusual notation. What is wrong with y'''?
     
  4. Aug 3, 2013 #3
    Your suggestion worked, I find it odd that leaving out x' makes it work though.

    The TI-89 can only do DE's up to the second degree. Would it help if I explained the method in full?

    Thanks for your help.
     
    Last edited: Aug 3, 2013
  5. Aug 4, 2013 #4

    mfb

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    Hmm... can it solve coupled DEs?

    z=y', z''+3z'+2z-5y=sin(2t)

    dx/dx=1
     
  6. Aug 4, 2013 #5
    No, it can't. I see what you're doing though, and its very similar to the method I am trying to use. In my method:

    y1 = y, y2 = y', y3 = y''...yn = y ^(n-1).

    From these:

    y'1 = y' = y2, y'2 = y'' = y3...y'(n) = y^n.

    This gives the system:

    y'1 = y2
    y'2 = y3

    My example from earlier:

    Ex: y''' + 3y'' + 2y' - 5y = sin(2t)

    Can be written as:

    y'(subscript 3) = 5y(subscript 1) - 2y(subscript 2) -3y(subscript 3) + sin(2t)

    I'm puzzled as to how to enter this in the calculator though.
     
  7. Aug 4, 2013 #6
    I understand I could graph this, but how would that help me?
     
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