Question

If one of the diameters of the circle $x^2+y^2–2x–6y+6=0$ is a chord of another circle $‘C^{\prime }$ whose center is at $(2,1)$, then its radius is

Answer 1

Distance between $(1,3)$ and $(2,1)$ is $\sqrt{5}$.
$\therefore (\sqrt{5}{)}^2+(2{)}^2=r^2\Rightarrow r=3$