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Math Help - [SOLVED] Rearrange to solve

  1. #1
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    [SOLVED] Rearrange to solve

    Okay I feel dumb asking this, I should know this, but it's been so long since I've bothered to use any algebra I've completely forgotten how it would be done.

    Consider this equation.

    a = b / (b + c)

    Pretend we have a value for a and c, how would you rearrange this to find b? It being on both the top and bottom of the division is what's confusing me.

    I did this but I know it's completely wrong:

    a * c = b /b

    but that would mean

    a * c = 1

    !!!

    Can somebody point out what I'm doing wrong?

    Cheers
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  2. #2
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by marclurr View Post
    Okay I feel dumb asking this, I should know this, but it's been so long since I've bothered to use any algebra I've completely forgotten how it would be done.

    Consider this equation.

    a = b / (b + c)

    Pretend we have a value for a and c, how would you rearrange this to find b? It being on both the top and bottom of the division is what's confusing me.

    I did this but I know it's completely wrong:

    a * c = b /b

    but that would mean

    a * c = 1

    !!!

    Can somebody point out what I'm doing wrong?

    Cheers
    Those brackets mean you have to multiply a by both terms inside it:

    a*(b+c) = ab+ac
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  3. #3
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    Would it make any difference if the brackets werent there? I just included them to make it clear that they were both on the 'bottom' of the division

    cheers
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  4. #4
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    Hi there, consider these steps.

    a=\frac{b}{b+c}

    I like to flip both sides to get

    \frac{1}{a}=\frac{b+c}{b}

    now working on the RHS

    \frac{1}{a}=\frac{b}{b}+\frac{c}{b}

    \frac{1}{a}=1+\frac{c}{b}

    now we only have 1 b so we can rearrange, have a go from here....





    my answer is

    b=\frac{c}{\frac{1}{a}-1}
    Last edited by pickslides; May 11th 2009 at 02:43 PM. Reason: typo
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  5. #5
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    Ahah that's what I was thinking of. I just couldn't remember that step :\ Thanks a lot
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