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# Partial Fraction Help Watch

1. Hi, I'm having trouble understanding why substituting does not give me the correct answer to this problem:

2x^2 + x + 1
--------------------
(x -3 ) (2x^2 + 1)
=
A Bx+C
----- + ----------
(x-3) (2x^2+1)

therefore 2x^2 + x + 1 = A(2x^2 + 1) + (Bx + C)(x - 3)

if we let x = 3, you get A = 22/19

if we let x = 0, you get 1 = A - 3C

3C = A - 1

As A = 22/19

3C = (22/19) - 1

3C = 3/19

C = 3/57

which the answer in my book tells me is incorrect. I can equate coefficients but I don't understand why using this method I get a wrong answer.

Thanks
2. It seems fine to me. What does the book say? I've got an inkling that you've just not noticed that .
3. thanks a lot for taking your time to help me, i think you were right and i just didn't realise 3/57 = 1/19 . it makes sense now
22/19(x-3) + 1-6x/19(2x^2 + 1)

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Updated: December 16, 2010
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