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Math Help - Help in rearanging an equation.

  1. #1
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    Help in rearanging an equation.

    I couldn't figure out how to rearrange so i looked at the answer but it still didnt help.

    If V = 12R / (r + R) , then R =

    Vr / (12 - V)

    We have to rearrange the equation to make R the subject.
    Start by cross multiplying by (r + R); V (r + R) = 12R
    Multiply out the bracket Vr + VR = 12R

    I pulled this off a website, I can't figure out how they get to Vr + VR=12R
    but I cant figure out how to get from that to Vr/(12-V)
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  2. #2
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    Quote Originally Posted by immunofort View Post
    I couldn't figure out how to rearrange so i looked at the answer but it still didnt help.

    If V = 12R / (r + R) , then R =

    Vr / (12 - V)

    We have to rearrange the equation to make R the subject.
    Start by cross multiplying by (r + R); V (r + R) = 12R
    Multiply out the bracket Vr + VR = 12R

    I pulled this off a website, I can't figure out how they get to Vr + VR=12R
    but I cant figure out how to get from that to Vr/(12-V)
    The can't. Do you mean can??

    Vr + VR = 12R

    => V r = 12R - V R

    Factorise the right hand side (R is a common factor):

    => V r = R (12 - V)

    Divide both sides by (12 - V) to isolate R:

    V r/(12 - V) = R. Viola!
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  3. #3
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    Yeah i did mean can and thanks for that. It seems so simple once i realized that i had to factorise.
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