$A\left(x_1, y_1\right)$ is the internal centre of similitude and $\mathrm{B}\left(x_2, y_2\right)$ is the external centre of similitude of two circles $C_1$ and $C_2$ whose centres are $\mathrm{P}(\alpha, \beta)$ and $\mathrm{Q}(\gamma, \delta)$ respectively. If $\mathrm{PA}=3, \mathrm{AB}=5, \mathrm{QB}=2$, then ratio of the radii of the two circles is