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

  1. #1
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    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.
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  2. #2
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    \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?
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  3. #3
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    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.
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  4. #4
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    Quote Originally Posted by paulbk108 View Post
    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  s^2-s+2.5

    you'll need to remove the space here [ math] for the code to work
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  5. #5
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    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...
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  6. #6
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    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 \frac{a}{m} + \frac{b}{n} = an + \frac{bm}{mn} or \frac{a}{m} + \frac{b}{n}= \frac{an + bm}{mn}

    I knew you meant the second one

    You can also hit the 'thanks' button on any posts you find helpful....
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  7. #7
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    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.
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  8. #8
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    Yep

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