# Factoring transfer funtions

1. May 6, 2012

### FrankJ777

Hi all. I'm trying to relearn S-plane analysis and filter transfer functions. What I'm having problems with is simple algebra i think, because it's been a while. Right now I've been reading http://www.ee.up.ac.za/main/_media/en/undergrad/subjects/eli220/polezero.pdf. What I'm confused about, among other things, is factoring the transfer function H(s).
In their example:

H(s) = $\frac{2s + 1}{(s^2 + 5S + 6)}$

factored

H(s) = $\frac{1}{2}$ $\frac{s+1/2}{(s+3)(s+2)}$

I don't understand how they get that. The way I see it, because:
2s+1 = 2(s+1/2)
and
$s^{2}$+5s+6 = (s+3)(s+2)
so

H(s) = $\frac{2s + 1}{(s^2 + 5S + 6)}$ = $\frac{2}{1}$ $\frac{s+1/2}{(s+3)(s+2)}$

Also It seems that:

$\frac{2s + 1}{(s^2 + 5S + 6)}$ ≠ $\frac{1}{2}$ $\frac{s+1/2}{(s+3)(s+2)}$

So I guess what I don't understand is why it seems that instead of factoring out 2 from the numerator, we are dividing the numerator by 2 and multiplying the denominator by 2.

Can someone please set me straight. I know I did this a few years ago and it seemed to make more sense then, than it does now.

Thanks a lot.

2. May 6, 2012

### Staff: Mentor

Hi FrankJ777. The explanation is quite simple: you are right and they are wrong.

3. May 7, 2012

### FrankJ777

Really? I hope that's the case. Too bad I wasted several study hours trying to get it.

Thanks