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Thread: Limit of Infinity

  1. #1
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    Limit of Infinity

    limit -x^5 + x - 1 as x goes to infinity

    Can I add infinity?

    -(infinity)^5 + infinity - 1 = -infinity + infinity (is it now positive or negative infinity?)
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  2. #2
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    Re: Limit of Infinity

    Hey joshuaa.

    Have you studied limits?
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    Re: Limit of Infinity

    yes but i am confused cuz the dr. says infinity - infinity is indeterminate. so will i add them or i cannot?
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  4. #4
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    Re: Limit of Infinity

    Quote Originally Posted by joshuaa View Post
    limit -x^5 + x - 1 as x goes to infinity

    Can I add infinity?

    -(infinity)^5 + infinity - 1 = -infinity + infinity (is it now positive or negative infinity?)
    You can't add infinities...infinity is not a number. But we can still do a comparison. Which is bigger for large numbers (not infinite ones), x^5 or x?

    -Dan
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    Re: Limit of Infinity

    Quote Originally Posted by topsquark View Post
    You can't add infinities...infinity is not a number. But we can still do a comparison. Which is bigger for large numbers (not infinite ones), x^5 or x?
    Better is to write -x^5+x = x(1-x^4) \to \infty \cdot (-\infty) = -\infty
    Or -x^5+x > -x^5 (where x > 0).
    Last edited by Archie; Jan 10th 2017 at 07:58 PM.
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    Re: Limit of Infinity

    From precalculus, recall the end behavior of an odd-degree polynomial with a negative leading coefficient.

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    Re: Limit of Infinity

    thanks guys
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