Answer
See image and solution
Work Step by Step
$f=\frac{r}{2}$
$\frac{1}{d_o}+\frac{1}{d_i}=\frac{1}{f}$
$d_i=\frac{1}{\frac{1}{f}-\frac{1}{d_o}}=\frac{1}{\frac{2}{r}-\frac{1}{d_o}}=\frac{rd_o}{2d_o-r}$
$m=\frac{h_i}{h_o}=-\frac{d_i}{d_o}=\frac{r}{r-2d_o}$
If $d_o>r$, $|m|<1$
If $f1$