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Math Help - Another differentiable Equation question

  1. #1
    Member CalcGeek31's Avatar
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    Another differentiable Equation question

    ax^2 + 1/3, x> 1
    f(x)=
    bx -10/3, x<1

    If the function is differentiable, find the sum of a + b

    I got that a+ 1/3 = b - 10/3

    Where do I go from there?
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  2. #2
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    skeeter's Avatar
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    you did the f(x) is continuous part ...


    need to do this, too, to get the second equation.

    \lim_{x \to 1^-} f'(x) = \lim_{x \to 1^+} f'(x)
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  3. #3
    Member CalcGeek31's Avatar
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    Ok, then I get 2a = b, so do I plug that back in to the original equations that were set equal to one another?



    EDIT:

    I ended up getting 11
    Last edited by CalcGeek31; January 5th 2009 at 02:54 PM.
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  4. #4
    Flow Master
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    Quote Originally Posted by CalcGeek31 View Post
    Ok, then I get 2a = b, so do I plug that back in to the original equations that were set equal to one another?



    EDIT:

    I ended up getting 11 Mr F says: Correct.
    For the record: Now you solve the following equations simultaneously for a and b:

    a + \frac{1}{3} = b - \frac{10}{3} .... (1)

    2a = b .... (2)

    Then you calculate the value of a + b.

    You get what you got.
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