Question Number 49976 by ajfour last updated on 12/Dec/18
Commented by ajfour last updated on 13/Dec/18
$${Thanks}\:{Sir},\:{i}'{ll}\:{better}\:{this}\:{question}. \\ $$
Commented by ajfour last updated on 12/Dec/18
$${Find}\:{r}. \\ $$
Commented by mr W last updated on 12/Dec/18
$$\frac{{R}−{r}}{{r}}=\frac{{r}}{\mathrm{2}{R}−{r}} \\ $$$$\mathrm{2}{R}^{\mathrm{2}} −\mathrm{3}{Rr}+{r}^{\mathrm{2}} ={r}^{\mathrm{2}} \\ $$$$\Rightarrow{r}=\frac{\mathrm{2}{R}}{\mathrm{3}} \\ $$