If $L_1, L_2$ and $L_3$ are the chords of contact of the three points $(2,0),(1,-2)$ and $(4,4)$ respectively with respect to the circle $x^2+y^2=3$, then $L_1, L_2$ and $L_3$ are

The combined equation of the direct common tangents of the circles $x^2+y^2+2 x=0$ and $x^2+y^2-2 y-3=0$

If $(h, k)$ is the centre of the circle which passes through the origin and cuts the circles $x^2+y^2+4 x+6 y+12=0$ and $x^2+y^2+4 x-6 y+9=0$ orthogonally, then $k-2 h=$

If $(-1,-1)$ is the radical centre of the circles $x^2+y^2+2 g x-4 y+4=0, x^2+y^2+6 x+2 f y+12=0$ and $x^2+y^2+10 y+20=0$, then $g-f=$