If the radical axis of the circles $x^2+y^2+2 g x+2 f y+c=0$ and $2 x^2+2 y^2+3 x+8 y+2 c=0$ touches the circle $x^2+y^2+2 x+2 y+1=0$, then

After the coordinate axes are rotated through an angle $\frac{\pi}{4}$ in the anti-clockwise direction without shifting the origin, if the equation $x^2+y^2-2 x-4 y-20=0$ transforms to $a x^2+2 h x y+b y^2+2 g x+2 f y+c=0$ in the new coordinate system, then

$$ \left|\begin{array}{lll} a & h & g \\ h & b & f \\ g & f & c \end{array}\right|= $$

If the circles $x^2+y^2+5 k x+2 y+k=0$ and $2 x^2+2 y^2+2 k x+3 y-1=0, k \in R$ intersect at points $P$ and $Q$ then the line $4 x+5 y-k=0$ passes through $P$ and $Q$ for

The slope of one of the direct common tangents drawn to the circles $x^2+y^2-2 x+4 y+1=0$ and $x^2+y^2-4 x-2 y+4=0$ is