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P3 May 2002 Q4b - Integration watch

1. Ok, i know there are loads of topics on P3 at the moment but I'm really stuck!

f(x) = A + B/(1+x) + C(3-x)

I found A,B and C to be -1, 1/2 and 5/2, but when i put these in and integrate between limits of 2 and 0, I'm not getting the right answer, which apparantly is -2 + 3ln3 (this isn't from an official mark scheme though). I get the -2 but not the 3 ln3.

Help!

Emma x x x
2. We have a P3 help thread, as well as a whole Maths subforum, but people still don't post in them.

Anyway, if you integrate that lot, you should get [-x + 2.5 ln |1+x| - 0.5 ln |3-x|]. Stick in 2, and you get (-2 + 2.5 ln 3 - 0.5 ln 1) = -2 + 2.5 ln 3.

Stick in 0, and you get (-0 + 2.5 ln 1 - 0.5 ln 3) = -0.5 ln 3

(-2 + 2.5 ln 3) - (-0.5 ln 3) = -2 + 3 ln 3 as required.
3. Sorry, I didn't notice the maths subforum and I wanted the thread to get noticed as I was really stuck and didn't know if people checked the end of all the threads.

Thank you though, I'd made a stupid mistake! (as usual)

Emma x x x

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