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Math Help - Simple "finding the domain" review

  1. #1
    DJM
    DJM is offline
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    Simple "finding the domain" review

    Technically I'm taking Calculus, but this is still in the range of Algebra I believe.

    The question is:

    3x+5
    over
    x^2+9x+20

    And all we have to do is state the intervals for the domain. So I have (-INF, -6],[-3,INF).

    But it's asking for three intervals, and I'm not sure what to put in the third one.

    We're using an online system,, so it's possible it could be a bug I suppose, but if not, I'm not sure what I'm missing.
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  2. #2
    MHF Contributor red_dog's Avatar
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    f(x)=\frac{3x+5}{x^2+9x+20}

    The condition is x^2+9x+20\neq 0

    x^2+9x+20=0\Rightarrow x_1=-5, \ x_2=-4

    Then x\in\mathbb{R}-\{-5,-4\}

    or x\in(-\infty,-5)\cup(-5,-4)\cup(-4,\infty)
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