# Math Help - Factorising problems

1. ## Factorising problems

I have an example:

$\frac{1}{(s^2+1)(s+2)^2}=$
$\frac{As+B}{s^2+1}+\frac{C}{(s+2)^2}+\frac{D}{s+2}$

Now, what bothers me here is that i don't understand when to use $As+B$ and when just $A$.

I read that it has something to do with real square roots, but i didn't get it.

2. Originally Posted by Pinsky
I have an example:

...
Now, what bothers me here is that i don't understand when to use $As+B$ and when just $A$.

I read that it has something to do with real square roots, but i didn't get it.
Have a look here: Partial fraction - Wikipedia, the free encyclopedia

Especially at

1.3. An irreducible quadratic factor in the denominator