Question 665748
The total resistance R of two resistors in parallel is given R=(1)/(1/R1+1/R2) where R1 is the resistance of the first and R2 the resistance of the second.  Solve the equation for R1 and simplify.
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1/R = 1/R1 + 1/R2
1/R1 = 1/R - 1/R2 = (R2 - R)/R*R2
R1 = R*R2/(R2 - R)