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Math Help - ilimts w/ result being infinity minus infinity

  1. #1
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    ilimts w/ result being infinity minus infinity

    I solved had two limits and I was adding them together, the fist come out to infinity and the second negative infinity giving me infinity - infinity What is that? I know normally you use l'hopital's rule but since it's two limits I don't know what to do.
    Limit A= infinity and Limit B=negative infinity The question is what is limit A+limit B I would post the exact problem but It might be graded.
    Last edited by Amberosia32; March 17th 2010 at 07:09 AM.
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  2. #2
    Super Member General's Avatar
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    Quote Originally Posted by Amberosia32 View Post
    I solved had two limits and I was adding them together, the fist come out to infinity and the second negative infinity giving me infinity - infinity What is that? I know normally you use l'hopital's rule but since it's two limits I don't know what to do.
    Post the problem !!
    How in earth we will know how to solve these limits if we did not see them ?
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  3. #3
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    In general, if f(x)- g(x) goes to "infinity- infinity", then e^{f(x)- g(x)}= \frac{e^{f(x)}}{e^{g(x)}} goes to "infinity over infinity" and you can apply L'Hopital's rule directly. If the imit of that is L then the limit of the original is ln(L).

    However General's point is well taken- a specific limit problem may have special properties that make it easier than the general situation. Typically, multiplying "numerator and denominator" by f(x)+ g(x) will help.
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