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Math Help - Possible to use analytic methods on lim x-->-2 x^2/(x+2) ?

  1. #1
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    Possible to use analytic methods on lim x-->-2 x^2/(x+2) ?

    Evaluate:


    I understand the answer is negative infinity but only by using the table method. Is there an analytic method possible?
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  2. #2
    A Plied Mathematician
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    Well, the numerator is always positive, right? And if x < -2, which it is, then the denominator is always negative. Since the numerator is bounded below by 4, and the denominator is going to zero, the limit is negative infinity.

    How's that?
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  3. #3
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    Since I couldn't factor and even the derivative is undefined at -2, I just wanted to make sure there wasn't anything else I could do.
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  4. #4
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    The limit has the form \frac{4}{0}. This is not an indeterminate form. So no special "tricks" are needed. A one sided limit in this case will always be positive or negative infinity - you just need to check which.
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  5. #5
    MHF Contributor FernandoRevilla's Avatar
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    Perhaps you are thinking about the L'Hopital's rule. In such a case, take into account that

    \displaystyle\lim_{x\to -2^-}\;x^2=4\;,\quad\displaystyle\lim_{x\to -2^-}(x+2)=0

    so, the corresponding hypothesis are not satisfied.


    Edited: Sorry, I didn't see DrSteve's post.
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