## Algebra and Trigonometry 10th Edition

$R_1\geq 2$
$R = \frac{1}{\frac{1}{R_1}+\frac{1}{R_2}}=\frac{R_1R_2}{R_1+R_2}$ Put $R_2=2$ and solve for $R_1$ when R >= 1 $\frac{2R_1}{R_1+2}\geq 1$ $2R_1\geq R_1+2$ $R_1\geq 2$