# When to use partial fraction?

1. Mar 14, 2009

1. The problem statement, all variables and given/known data

do we look at the nominator or the denominator? are we trying to separate them? factoring them?

thanks

2. Mar 14, 2009

### tiny-tim

The denominator. And you factor it.

3. Mar 14, 2009

so let's say i have this long equation in denom.

$$\frac{1}{(s^2+1)(s^2+4s-12)}$$

i can factor one of them to look like:

$$\frac{1}{(s^2+1)(s+6)(s-4)}$$

but then how do I know if I should use A +B or As+B, Cs+D, etc..?

4. Mar 14, 2009

### tiny-tim

erm … nooo!
sorry, not following you …

for a linear denominator, it's just a number on the top,

for a quadratic denominator, it's a linear top

5. Mar 14, 2009

haha made a mistake... so with that, do i use As+ B?

what if it's (s^2+2)(s^2+3)(s^2+5), ie, several s squares?

6. Mar 14, 2009

if was supposed to be a (s+6)(s-2)....

7. Mar 14, 2009

### tiny-tim

each one has a linear top
each one has a number on the top

8. Mar 14, 2009

ok,

taking this example again: (s^2+2)(s^2+3)(s^2+5)

would it be: 1 = (As+B)/(s^2+2)(s^2+3)(s^2+5) + (Cs+D)/(s^2+2)(s^2+3)(s^2+5) + (Es+F)/(s^2+2)(s^2+3)(s^2+5) ?

9. Mar 14, 2009

### tiny-tim

uhh?

it's 1/(s2+2)(s2+3)(s2+5)

= (As+B)/(s2+2) + (Cs+D)/(s2+3) + (Es+F)/(s2+5)

10. Mar 14, 2009

haha brain fart on my part(i hope)

thanks

11. Mar 14, 2009

### tiny-tim

12. Mar 14, 2009

are you a math teacher?
if you don't mind me asking!

13. Mar 14, 2009

### tiny-tim

i'm just a little goldfish …

trying to make sense of the bowliverse!

14. Mar 14, 2009