Integration of an inverse function

[iceman_ch]

Homework Statement

\int\frac{4}{x(x+3)}

Homework Equations

The Attempt at a Solution

I can get to s certain point and I know I need to do substitution but, everytime I try a substitution it just creates a more difficult problem.

4\int(x^{-1}(x+3)^{-1})

I've tried substitution x^-1 for U and using (x+3)^-1 for dv but, none of it works. If someone could give me a gentle nudge it would be appreciated.

Thanks

 

[gabbagabbahey]

This problem is an ideal candidate for the method of "partial fractions".

Try decomposing \frac{1}{x(x+3)} into the form \frac{A}{x}+\frac{B}{x+3} where A and B are constants you need to determine.

 

[iceman_ch]

OH man so obvious. Your the man thank you so much. I havn't had a math class in over a year and now I'm taking diff eq. Bad idea you should definately keep them all together.

 

[HallsofIvy]

And, when talking about functions, be careful to distinguish between "reciprocal" and "inverse" functions!