A line meets the circle $x^2+y^2-4 x-4 y-8=0$ in two points $A$ and $B$. If $P(2,-2)$ is a point on the circle such that $P A=P B=2$, then the equation of the line $A B$ is

If the centre $(\alpha, \beta)$ of a circle cutting the circles $x^2+y^2-2 y-3=0$ and $x^2+y^2+4 x+3=0$ orthogonally lies on the line $2 x-3 y+4=0$, then $2 \alpha+\beta=$

The radius of a circle $C_1$ is thrice the radius of another circle $C_2$ and the centres of $C_1$ and $C_2$ are $(1,2)$ and $(3,-2)$ respectively. If they cut each other orthogonally and the radius of the circle $C_1$ is $3 r$, then the equation of the circle with $r$ as radius and $(1,-2)$ as centre is

The slope of a common tangent to the circles $x^2+y^2=16$ and $(x-9)^2+y^2=16$ is