Integration partial fractions

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Feb 28th 2010, 08:22 AM
wolfhound

Integration partial fractions

Hello,
could someone tell me where I made a mistake on this partial fraction problem
Please
Feb 28th 2010, 08:32 AM
Archie Meade

Quote:

Originally Posted by wolfhound

Hello,
could someone tell me where I made a mistake on this partial fraction problem
Please

hi wolfhound,

$\frac{A}{x}+\frac{B}{x^2+1}=\frac{1}{x^3+x}$

$\frac{A\left(x^2+1\right)+Bx}{x\left(x^2+1\right)} =\frac{1}{x^3+x}$

$\frac{Ax^2+A+Bx}{x^3+x}=\frac{1}{x^3+x}$

$x\left(Ax+B\right)+A=x(0)+1$

$A=1$

$(1)x+B=0\ \Rightarrow\ B=-x$
Feb 28th 2010, 08:39 AM
wolfhound

Hi archie
Oh so I dont actually get a value for B? except B=-x?
someone said I should input i in to solve these also
when should I take a coefficient as x and not a value please?
Feb 28th 2010, 08:47 AM
Archie Meade

Hi wolfhound,

sometimes there will be an x-component of the A and B values.
They are not necessarily "constants".

They are "numerators".

They only end up being constants sometimes.

If you add those two resulting fractions together,
you will see that the result is the original fraction you wanted to integrate.

since the sum of the resulting fractions is the original,
you can more conveniently integrate the partial fractions.

The trick is....

if the numerator of the original fraction is a constant,
then you can write it as "constant + (0)x"
Feb 28th 2010, 08:55 AM
wolfhound

I see,
I am going to practice some more now
Thanks

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