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Math Help - Limit help with conjugates (i think) :)

  1. #1
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    Limit help with conjugates (i think) :)

    There is something im not getting with this limit and its like a roadblock for the rest of the Homework because i been getting similar results on the next few problems.

    lim (X-1) / [sr(x+3)-2]
    x-1

    answer is 4

    I assume i must use the conjugate method and mult the top and bottom by (srx+3)+2 but doing that with the dem i get [x-3]-4 on the bottom which cant work because the dem. can't be zero!

    since i thought it might be a trick question i tied taking the conj of the top but i end up with the anwser 1/4 which is wrong too.

    so how do i do this? thanks

    edit really sorry i forgo tthe SR at the end of hte problem
    Last edited by Kevfactor; January 14th 2012 at 09:23 PM.
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  2. #2
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    Crna Gora
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    Re: Limit help with conjugates (i think) :)

    Quote Originally Posted by Kevfactor View Post
    There is something im not getting with this limit and its like a roadblock for the rest of the Homework because i been getting similar results on the next few problems.

    lim (X-1) / [sr(x+3)-2]
    x-1

    answer is 4

    I assume i must use the conjugate method and mult the top and bottom by (srx+3)+2 but doing that with the dem i get [x-3]-4 on the bottom which cant work because the dem. can't be zero!

    since i thought it might be a trick question i tied taking the conj of the top but i end up with the anwser 1/4 which is wrong too.

    so how do i do this? thanks

    edit really sorry i forgo tthe SR at the end of hte problem
    \displaystyle \lim_{x \to 1} \frac{x-1}{\sqrt{x+3}-2}=\displaystyle \lim_{x \to 1} \frac{x-1}{\sqrt{x+3}-2} \cdot \frac {\sqrt{x+3}+2}{\sqrt{x+3}+2}=\displaystyle \lim_{x \to 1} \frac{(x-1)(\sqrt{x+3}+2)}{x+3-4} \Rightarrow

    \Rightarrow \displaystyle \lim_{x \to 1} (\sqrt{x+3}+2)=4
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  3. #3
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    Re: Limit help with conjugates (i think) :)

    thanks ya i see what i did now and the other problems

    im a bit rusty on factoring( only did it once in precalc) and after a lot of head banging i finally remembered i can drop the brakets if its an addition term. i still didnt remember it on that problem tho.
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