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Math Help - limits

  1. #1
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    limits

    could someone please explain to me how to do these?

    3x^2 + 2x + 1
    limx --------------
    x^2 + x - 3


    x^2 + 1
    limx ---------
    x^2 - 1



    thank you
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  2. #2
    MHF Contributor kalagota's Avatar
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    Quote Originally Posted by hollies_yardbirds_kinks View Post
    could someone please explain to me how to do these?

    3x^2 + 2x + 1
    limx --------------
    x^2 + x - 3


    x^2 + 1
    limx ---------
    x^2 - 1



    thank you
    where do we approach x?
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  3. #3
    Moo
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    Hello !
    Quote Originally Posted by hollies_yardbirds_kinks View Post
    could someone please explain to me how to do these?

    3x^2 + 2x + 1
    limx --------------
    x^2 + x - 3


    x^2 + 1
    limx ---------
    x^2 - 1



    thank you
    When you have a division of polynomials (and limit to infinity), there are a few possible ways to solve the limit :
    - l'hospital's rule
    - find the greatest power of x in the numerator and the denominator and factor in the numerator and denominator. For example, if you have x+1, factor by x : x^2+1=x^2 \left(1+\frac 1{x^2}\right). x^2-1=x^2 \left(1-\frac 1{x^2}\right)
    So you can simplify by x. What's left is in general a finite limit

    - know some rules : if the degree of the polynomial in the numerator is greater than the one of the denominator, the limit is \infty (the sign depends on the leading coefficient)
    if the degree of the polynomial in the numerator is smaller than the one of the denominator, the limit is 0.
    if they're the same, the limit is the quotient of the leading coefficients.
    These rules derive from the point just above


    Sidenote : Leading coefficient : Definition
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