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#34614

equations

formulas

hard

90 sec

The total resistance $R$ of two resistors $R_{1}$ and $R_{2}$ connected in parallel is given by the formula $\frac{1}{R} = \frac{1}{R _{1}} + \frac{1}{R _{2}}$ . Which equation correctly expresses $R_{1}$ in terms of $R$ and $R_{2}$ ?

A.

$R_{1} = \frac{R R _{2}}{R _{2} - R}$

B.

$R_{1} = R_{2} - R$

C.

$R_{1} = \frac{R _{2} - R}{R R _{2}}$

D.

$R_{1} = \frac{1}{R} - \frac{1}{R _{2}}$