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http://i5.photobucket.com/albums/y160/bornstubborn101/circuit3.jpg

This is the circuit. Basically i need to calculate the two resistors that would make up the potentiometer at VR1 to give a voltage of 3V.

I was going to use

VR1 = R2/(R1+R2)*Vs

The make:

R1= VR1/Vs*(R1+R2)

However apaprently this is wrong due to the +15V and the -15V inputs and that i need to use this equation.

R1=(0.5- VR1/VS)*(R1+R2)

I don;t know where this equation comes from so i can;t really use it in my report. Does anyone know where this equation comes from and how i can explain it.

Thanks

This is the circuit. Basically i need to calculate the two resistors that would make up the potentiometer at VR1 to give a voltage of 3V.

I was going to use

VR1 = R2/(R1+R2)*Vs

The make:

R1= VR1/Vs*(R1+R2)

However apaprently this is wrong due to the +15V and the -15V inputs and that i need to use this equation.

R1=(0.5- VR1/VS)*(R1+R2)

I don;t know where this equation comes from so i can;t really use it in my report. Does anyone know where this equation comes from and how i can explain it.

Thanks

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