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Math Help - Make x the subject

  1. #1
    Newbie
    Joined
    Feb 2009
    Posts
    4

    Make x the subject

    Hi

    Where am I going wrong in trying to rearrange this:

    <br />
\frac{x+a}{x+b} = c<br />

    <br />
x+a = c(x+b)<br />

    <br />
\frac{x+a}{c} = x+b<br />

    <br />
\frac{x+a}{c}-b = x<br />

    <br />
x+a - cb = xc<br />

    <br />
a - cb = xc - x<br />

    <br />
\frac{a-cb}{c} = x - x<br />

    Thanks
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  2. #2
    Super Member Failure's Avatar
    Joined
    Jul 2009
    From
    Zürich
    Posts
    555
    Quote Originally Posted by preid View Post
    Hi

    Where am I going wrong in trying to rearrange this:

    <br />
\frac{x+a}{x+b} = c<br />

    <br />
x+a = c(x+b)<br />

    <br />
\frac{x+a}{c} = x+b<br />

    <br />
\frac{x+a}{c}-b = x<br />

    <br />
x+a - cb = xc<br />

    <br />
a - cb = xc - x<br />
    Ok thus far, although a bit longwinded. But now factor out x on the right side first:

    a-cb=x(c-1)
    and divide both sides by c-1 to get:

    \frac{a-cb}{c-1}=x
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