A. x2+y2=r2

B. x2+y2=4r2

C. x2+y2=8r2

D. x2+y2=r2/2

The centres of the circles are (a, c) and (b, c) and their radical axis is the y-axis. The radius of one of the circle is r. The radius of the other circle is

The tangents drawn from the origin to the circle x^{2}+y^{2}-2rx-2hy+h^{2}=0 are perpendicular if

If x^{2}+y^{2}-2x+3y+k=0 and x^{2}+y^{2}+8x-6y-7=0 cut each orthogonally, the value of k must be

The equation of the circle passing through the intersection of the circles x^{2}+y^{2}=2ax and x^{2}+y^{2}=2by and having its centre on the x/a-y/b=2 is

If O is the origin and OP, OQ are the tangents to the circles x^{2}+y^{2}+2gx+2fy+c=0 then the circumcentre of the ΔOPQ is