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Homework Help: Partial fractions: different results from two methods

  1. Sep 25, 2011 #1

    Multiply by common denominator gives:


    System of equations gives

    [tex]\Rightarrow A=-\frac{5}{2}, B=\frac{3}{2}, C=-1

    However, "hand over" method gives:
    [tex][x=1]\Rightarrow A=\frac{
    -2(1)^2-1-3}{(1+1)(1+2)}=\frac{-6}{6}=-1[/tex][tex][x=-1]\Rightarrow B=\frac{
    -2(-1)^2+1-3}{(-1-1)(-1+2)}=\frac{-4}{-2}=2[/tex][tex][x=-2]\Rightarrow C=\frac{

    Are both solutions correct, if so is that just a coincidence?
    Have I made any errors, if so where?
  2. jcsd
  3. Sep 25, 2011 #2


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    Homework Helper

    Looks like here's the problem. You forgot to include some integer coefficients. The system should be this:
    [tex]A + B + C = -2
    [/tex][tex]3A + B = -1
    [/tex][tex]2A - 2B - C = -3[/tex]
  4. Sep 25, 2011 #3
    Ahh yes. Thanks!
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