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Math Help - Integration and particular solutions

  1. #1
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    Integration and particular solutions

    I think there is something that I am missing because my answer is turning out to be wrong.

    Find the particular solution for the following differential given that it passes through (-1, -6).

    f ' (x) = 24x^2 - 4x + 5

    I can do it well without the negative number and my answer results in: y = 8x^3 - 2x^2 + 5x + 9

    Thanks...
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  2. #2
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    Quote Originally Posted by Googl View Post
    I think there is something that I am missing because my answer is turning out to be wrong.

    Find the particular solution for the following differential given that it passes through (-1, -6).

    f ' (x) = 24x^2 - 4x + 5

    I can do it well without the negative number and my answer results in: y = 8x^3 - 2x^2 + 5x + 9

    Thanks...


    It doesn't take too long to a maths student to realize that many times books/teachers are wrong, and perhaps this is

    one of those occasions: your answer is right according to what you say is the given data.

    Tonio
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  3. #3
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    Quote Originally Posted by tonio View Post
    It doesn't take too long to a maths student to realize that many times books/teachers are wrong, and perhaps this is

    one of those occasions: your answer is right according to what you say is the given data.

    Tonio
    My answer can't be right surely. What did you get? It is wrong. There have been many situations where I have failed a question in a similar format. Having a negative (-4x for example)
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  4. #4
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    No, both tonio and you are correct concerning the OP. Check:

    y = 8x^3 - 2x^2 + 5x + 9

    y' = 24 x^2 - 4x + 5 = f(x).

    Moreover, y(-1) = 8 (-1) - 2 (1) + 5 (-1) + 9 = -8 - 2 - 5 + 9 = -10 + 4 = -6, as required.

    Therefore, your answer in the OP is correct.
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  5. #5
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    Quote Originally Posted by Googl View Post
    My answer can't be right surely. What did you get? It is wrong. There have been many situations where I have failed a question in a similar format. Having a negative (-4x for example)

    You must be a beginning student and thus you seem to still believe that books and teachers are infallible. You're wrong: they

    can be, and many times are, wrong.

    Now, do not believe me: check your answer as you probably was taught and you'll see it fuflils the question's requirements.

    Tonio
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