# Require assistance with G=[5/s(s-1)]/[1+{2.5/s(s-1)}]

• Dec 7th 2010, 12:37 PM
paulbk108
Require assistance with G=[5/s(s-1)]/[1+{2.5/s(s-1)}]
Good day folks,

To repeat: the equation I am wrestling with is G=[5/s(s-1)]/[1+{2.5/s(s-1)}].

It simplifies to G = 5/[s^2-s+2.5].

I am a touch rusty with this stuff and have played with it for hours but to no avail. I know that x/y / w/z = xz/wy but still cannot get it to work.

I know once I see the working I will feel like a fool but for now it is just frustration.

Can someone please assist?

Regards.
• Dec 7th 2010, 12:55 PM
pickslides
$\displaystyle \displaystyle G = \frac{\frac{5}{s(s-1)}}{1+\frac{2.5}{s(s-1)}} = \frac{\frac{5}{s(s-1)}}{\frac{s(s-1)}{s(s-1)}+\frac{2.5}{s(s-1)}} = \frac{\frac{5}{s(s-1)}}{\frac{s(s-1)+2.5}{s(s-1)}} = \frac{5}{s(s-1)}\times \frac{s(s-1)}{s(s-1)+2.5}$

Can you finish it?
• Dec 7th 2010, 01:06 PM
paulbk108
I believe so:

= 5*[s(s-1)]/s(s-1)*s(s-1)*s(s-1)+2.5 = 5/s(s-1)+2.5 = 5/s^2-s+2.5 Thank you so much!

By the way - what software,add-on etc do you use to input that stuff in that format, rather than my ugly "normal" style?

Regards.
• Dec 7th 2010, 01:27 PM
pickslides
Quote:

Originally Posted by paulbk108
By the way - what software,add-on etc do you use to input that stuff in that format, rather than my ugly "normal" style?

None required, just wrap math tags around your symbols i.e. [ math] s^-s+2.5[/tex] gives $\displaystyle s^2-s+2.5$

you'll need to remove the space here [ math] for the code to work
• Dec 7th 2010, 01:39 PM
paulbk108
Interesting...I will have to have a practice at it.

One last query - in the denominator did you use the simple rule of a/m + b/n = an + bm/mn? Please excuse my ignorance here - I am just trying to clear up some issues...
• Dec 7th 2010, 01:51 PM
pickslides
Correct, I did apply this thinking.

You may want to consider using some brackets as what you have is ambiguous

i.e. a/m + b/n = an + bm/mn could be $\displaystyle \frac{a}{m} + \frac{b}{n} = an + \frac{bm}{mn}$ or $\displaystyle \frac{a}{m} + \frac{b}{n}= \frac{an + bm}{mn}$

I knew you meant the second one (Rock)

You can also hit the 'thanks' button on any posts you find helpful....(Rofl)
• Dec 7th 2010, 02:12 PM
paulbk108
Can this formula be used for more than two fractions? I have another that is 1 + [(s+2)/s] + [4/s(s-1)] that needs to be simplified. It simplifies to 4s(s+2)/s^2+1. Do I use the same method?

Regards.
• Dec 7th 2010, 05:47 PM
pickslides
Yep

a/m+b/n+p/q = (anq+bmq+pmn)/mnq