Two tangent lines l_1 and l_2 are drawn from the point (2,0) to the parabola 2 y^2=-x. If the lines l_1 and l_2 are also tangent to the circle…

Two tangent lines $\displaystyle l_1$ and $\displaystyle l_2$ are drawn from the point $\displaystyle (2,0)$ to the parabola $\displaystyle 2 \mathrm{y}^2=-x$. If the lines $\displaystyle l_1$ and $\displaystyle l_2$ are also tangent to the circle $\displaystyle (x-5)^2+\mathrm{y}^2=\mathrm{r}$, then $\displaystyle 17$ r is equal to \_\_\_\_.