# When to use partial fraction? (1 Viewer)

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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

#### tiny-tim

Homework Helper
do we look at the nominator or the denominator? are we trying to separate them? factoring them?
The denominator. And you factor it.

The denominator. And you factor it.
thanks for the answers!

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..?

#### tiny-tim

Homework Helper
i can factor one of them to look like:

$$\frac{1}{(s^2+1)(s+6)(s-4)}$$
erm … nooo!
but then how do I know if I should use A +B or As+B, Cs+D, etc..?
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

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

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?

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

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

#### tiny-tim

Homework Helper
what if it's (s^2+2)(s^2+3)(s^2+5), ie, several s squares?
each one has a linear top
if was supposed to be a (s+6)(s-2)....
each one has a number on the top

each one has a linear top
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) ?

#### tiny-tim

Homework Helper
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) ?
uhh?

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

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

uhh?

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

= (As+B)/(s2+2) + (Cs+D)/(s2+3) + (Es+F)/(s2+5)
haha brain fart on my part(i hope)

thanks

#### tiny-tim

Homework Helper

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

#### tiny-tim

Homework Helper
i'm just a little goldfish …

trying to make sense of the bowliverse!

i'm just a little goldfish …

trying to make sense of the bowliverse!
haha! well, thanks for the help!

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