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Homework Help: Evaluating limits with constant?

  1. Apr 17, 2012 #1
    1. The problem statement, all variables and given/known data
    Is there such a number b such that lim x->-2 (3x^2+bx+b+3)/(x^2+x-2) exists? If so, find b and the limit.

    2. Relevant equations
    lim x->-2 (3x^2+bx+b+3)/(x^2+x-2)

    3. The attempt at a solution
    for the denominator we have zeroes at x = 1 and -2. so we need to get rid of the -2 part right? set up (3x^2+bx+b+3)=0 and solve for b to get b = -3-3x^2/(x+1) which has b = 15 (which is what the answer book has). but if b = 15, the numerator just becomes 3x^2+15x+18 when factored go to (3x+18)(x+1) which doesnt cancel out with anything on the bottom. they also say that the limit is -1 but how??

    neeeeeevermind. got the factoring mixed up. limit is -1.
    Last edited: Apr 17, 2012
  2. jcsd
  3. Apr 17, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    You factored 3x^2+15x+18 wrong. Try that again.
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