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Homework Help: Partial fractions questions

  1. Jan 27, 2005 #1
    original question: [tex]\int[/tex] (x^2+2x-1)/(x(2x-1)(x+2))

    the following is from my math book:
    2A + B + 2C = 1
    3A + 2B - C = 2
    -2A = -1

    okay i understand everything the math has done up to this point, this is the point that i dont get:

    A = 1/2, B = 1/5, C = -1/10

    i think the book got A from solving this equation: -2A = -1

    I just want to know how the book got A, B, and C.
    Last edited: Jan 27, 2005
  2. jcsd
  3. Jan 27, 2005 #2
    If those are the values for A, B and C given in the book, apparently -2A=1 was supposed to be 2A=1. Otherwise all those values are wrong.

    (But what does that have to do with partial fractions?)
  4. Jan 27, 2005 #3
    my bad, it was a typo. it's suppose to be -2A = -1

    and it has to do with partial fractions because it's a partial fractions question.
  5. Jan 27, 2005 #4


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    Staff Emeritus
    Science Advisor
    Gold Member

    Sure, the question came from a partial fraction problem... but partial fractions have nothing to do with its solution.

    The problem is now purely algebraic: you have a system of equations with several unknowns. Do you remember anything from your algebra classes about solving them?
  6. Jan 27, 2005 #5

    nevermind, i got it. wow i cant believe i didnt get it. i was thinking too hard
    Last edited: Jan 27, 2005
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