## Algebra 2 Common Core

$R=\frac{r_{1}r_{2}}{r_{1}+r_{2}}$
We can isolate $R$ by dividing both sides by $(r_{1}+r_{2})$. We have $\frac{R(r_{1}+r_{2})}{(r_{1}+r_{2})}=\frac{r_{1}r_{2}}{(r_{1}+r_{2})}$ is $R=\frac{r_{1}r_{2}}{r_{1}+r_{2}}$.