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Math Help - Evaluate difference quotient.

  1. #1
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    Evaluate difference quotient.

    a) f(x) = 4 - 3x - x^2
    Diff. Quotient : ( f(3+h) - f(3) ) / h

    b) f(x) = (x+8) / (x+6)
    Diff. Quotient : ( f(x) - f(6) ) / x-6

    I understand how to do the problem, but for some reason I just can't get the right answer. I have come up with four different ones. Can someone do the math here for me? I can't see what I am doing wrong. If I have to, I'll post my work.
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  2. #2
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    Re: Evaluate difference quotient.

    It's not up to the forum members to do the math for you.

    If you show some workings we may then show you where to improve

    For the first one. Expand this out.

    \displaystyle \frac{(4 - 3( 3+h) - (3+h)^2)-(4 - 3\times 3 - 3^2)}{h} = \dots


    For the second one note that

    \displaystyle \frac{x+8}{x+6}= \frac{x+6+2}{x+6}= \frac{x+6}{x+6}+\frac{2}{x+6} = 1+\frac{2}{x+6}
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  3. #3
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    Re: Evaluate difference quotient.

    [(1 + 2/x+6) - (1 + 1/6)] / x-6
    Is that right then?
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  4. #4
    MHF Contributor Siron's Avatar
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    Re: Evaluate difference quotient.

    Yes that's right but try to simplify as much as possible if you have to.
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