$\sqrt{5}$

$2 \sqrt{5}$

$4 \sqrt{5}$

$5 \sqrt{2}$

$x^2+y^2-6 x+2 y-6=0$

$x^2+y^2-x+7=0$

$x^2+y^2+x-7=0$

$x^2+y^2+6 x-2 y-6=0$

$\left(-\frac{1}{2}, 0\right)$

$\left(\frac{5}{2}, 0\right)$

$\left(0, \frac{5}{2}\right)$

$\left(0,-\frac{1}{2}\right)$