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Math Help - transposing to calculate resitor values

  1. #1
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    transposing to calculate resitor values

    in a circuit for a potential divider which calculates voltage drops, i nned to transpose it so that i can calculate resistances.

    The existing formula is

    v=(R1/RT)(V)

    where v is voltage drop across a resistor (9.38 Volts) and V is source voltage(10 volts), R1=75k ohm, R2=5k ohm, RT=R1+R2. How would I make R1 the subject? Thanks

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    Frank
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  2. #2
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    Smile

    Hello
    v=\left (\frac{R_{1}}{R_{1}+R_{2}}  \right )V\Leftrightarrow v(R_{1}+R_{2})=R_{1}V\Leftrightarrow vR_{1}+vR_{2} =R_{1}V\Leftrightarrow vR_{1}-R_{1}V=-vR_{2}\Leftrightarrow R_{1}(v-V)=-vR_{2}, you know what to do next.
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  3. #3
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    Quote Originally Posted by Raoh View Post
    Hello
    v=\left (\frac{R_{1}}{R_{1}+R_{2}}  \right )V\Leftrightarrow v(R_{1}+R_{2})=R_{1}V\Leftrightarrow vR_{1}+vR_{2} =R_{1}V\Leftrightarrow vR_{1}-R_{1}V=-vR_{2}\Leftrightarrow R_{1}(v-V)=-vR_{2}, you know what to do next.
    I certainly do. Ta.

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    Frank
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