If the angle between the circles $x^2+y^2-2 x+k y+1=0$ and $x^2+y^2-k x-2 y+1=0$ is $\cos ^{-1}\left(\frac{1}{4}\right)$ and $k<0$, then the point which lies on the radical axis of the given circle is

If the circles $x^2+y^2-4 x+6 y+13-a^2=0$ and $x^2+y^2-10 x-2 y+17=0$ intersect in two distinct points, then ' $a$ ' is