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Math Help - Rearranging Equation

  1. #1
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    Rearranging Equation

    Im very-much out of practice... Almost feel guilty posting in 'Pre-University'

    I'm trying to rearrange this equation for a electronic regulator,

    <br />
Vout = (1.25 * ((1+R2)/R1)) + Iadj*R2<br />

    So that R2 is on its own. Im not sure what todo to cancel R2 on the left hand side...

    <br />
R1 * ((Vout - (Iadj * R2))/1.25) - 1 = R2<br />

    Not sure how to use the maths tags properly.

    Any help much appreciated.
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  2. #2
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    Quote Originally Posted by embob View Post
    Im very-much out of practice... Almost feel guilty posting in 'Pre-University'

    I'm trying to rearrange this equation for a electronic regulator,

    <br />
Vout = (1.25 * ((1+R2)/R1)) + Iadj*R2<br />

    So that R2 is on its own. Im not sure what todo to cancel R2 on the left hand side...

    <br />
R1 * ((Vout - (Iadj * R2))/1.25) - 1 = R2<br />

    Not sure how to use the maths tags properly.

    Any help much appreciated.
    So you want to solve for R_2...


    V_{\textrm{out}} = \frac{1.25(1 + R_2)}{R_1} + I_{\textrm{adj}}R_2

     = \frac{1.25 + 1.25R_2}{R_1} + I_{\textrm{adj}}R_2

     = \frac{1.25 + 1.25R_2}{R_1} + \frac{I_{\textrm{adj}}R_1R_2}{R_1}

     = \frac{1.25 + 1.25 R_2 + I_{\textrm{adj}}R_1R_2}{R_1}

     = \frac{1.25 + R_2(1.25 + I_{\textrm{adj}}R_1)}{R_1}.


    Now, solving for R_2...

    V_{\textrm{out}} = \frac{1.25 + R_2(1.25 + I_{\textrm{adj}}R_1)}{R_1}

    R_1V_{\textrm{out}} = 1.25 + R_2(1.25 + I_{\textrm{adj}}R_1)

    R_1V_{\textrm{out}} - 1.25 = R_2(1.25 + I_{\textrm{adj}}R_1)

    R_2 = \frac{R_1V_{\textrm{out}}}{1.25 + I_{\textrm{adj}}R_1}.
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  3. #3
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    Feb 2010
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    Thank you!

    Do you know any good tutorials for rearranging equations. I could do with going through a couple of hundred examples...
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