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Math Help - Re-arranging equation

  1. #1
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    Re-arranging equation

    Hi all,

    Just a quick question trying to re-arrange a formula.

    How do we do it when the subject we want is on both the top and the bottom in a fraction? An example would be something like the following.

    Make R the subject.


    N = \frac{RM}{S + R} or something similar.

    Any help is appreciated.
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Peleus View Post
    Hi all,

    Just a quick question trying to re-arrange a formula.

    How do we do it when the subject we want is on both the top and the bottom in a fraction? An example would be something like the following.

    Make R the subject.


    N = \frac{RM}{S + R} or something similar.

    Any help is appreciated.
    start by multiplying both sides by the denominator on the right. you get NS + NR = RM

    now how would you continue?
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  3. #3
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    yeah, I can get that far.

    From there you could divide by M which would result in R being on it's own on one side, but how do you get rid of the other R (part of NR)? That's the part I couldn't get. Typically to break it up you divide by N but then we're going backwards making the R which was on it's own \frac{R}{N}
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  4. #4
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Peleus View Post
    yeah, I can get that far.

    From there you could divide by M which would result in R being on it's own on one side, but how do you get rid of the other R (part of NR)? That's the part I couldn't get. Typically to break it up you divide by N but then we're going backwards making the R which was on it's own \frac{R}{N}
    how about first bringing all the guys with R's in them on one side, and everything else on the other?

    RM - NR = NS

    but then R is a common factor on the left

    R(M - N) = NS

    and so...
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  5. #5
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    Awesome,

    The obvious answer staring me in the face, I just couldn't see it

    Thanks for your help.


    (Oh and obviously we're deviding both sides by that factor leaving R alone).

    Thanks mate.
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  6. #6
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    Talking

    Quote Originally Posted by Peleus View Post
    yeah, I can get that far.
    FYI: If you've made some progress on an exercise, it will be helpful if you show that, so that the helpers don't repeat what you've already done. Thank you!
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