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Find lowest common denominator of these polynomials

  1. Oct 14, 2008 #1
    1. The problem statement, all variables and given/known data
    3/x^2+2x - 2/x^2+x-2 + 4/x^2(x-1)
    Find the lowest common denominator and solve.


    2. Relevant equations



    3. The attempt at a solution

    I factored x(x+2) - (x-1)(x+2) + x^2(x-1)

    It looks like (x+2), (x-1) are common but what to do with the x & x^2 left over?
    Thank you in advance.
     
  2. jcsd
  3. Oct 14, 2008 #2

    tiny-tim

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    Hi Makman! :smile:
    Nooo … you're looking at this the wrong way …

    Hint: the LCD of, say, 1/2*3 and 1/3*5 would be 2*3*5 :wink:
     
  4. Oct 14, 2008 #3
    Re: Lcd

    If I take your example and it was 1/6 + 1/15 my answer would be 7/30. 30 being the common denominator. As I understand it, 90 could be a common denominator but it is not the lowest.
    What should I do with the denominator in the original problem to make things more clear. I'm not cluing in. My apologies.
    Please help.
    Thank you.
     
  5. Oct 14, 2008 #4

    tiny-tim

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    ok … when you had 2*3 and 3*5, you needed to include everything the minimum number of times… that's 2*3*5.

    so when you have x(x+2) (x-1)(x+2) and x2(x-1), again you could just multiply everything, to give x(x+2)(x-1)(x+2)x2(x-1), but you can cut that down to … ? :smile:
     
  6. Oct 14, 2008 #5
    Re: Lcd

    I believe I got it. The L.C.D. would be x^2(x-1)(x+2). Is this correct?
     
  7. Oct 14, 2008 #6

    tiny-tim

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    :biggrin: Woohoo! :biggrin:
     
  8. Oct 14, 2008 #7
    Re: Lcd

    Thank you for your time and patience.:approve:
     
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