A. the centres are collinear

B. they are coaxial

C. they are concentric

D. none

The polar of the point (1, -2) w.r.t the circles x^{2}+y^{2}+6y+5=0 , x^{2}+y^{2}+2x+8y+5=0 are

The number of common tangents to the two circles x^{2}+y^{2}=4, x^{2}+y^{2}-8x+12=0 is

If (2, 6) is a centre of similitude for the-circles x^{2}+y^{2}=4 and x^{2}+y^{2}-2x-6y+9=0, the length of the common tangent of circles through it is

The radical axis of co-axial system of circle with the limiting points (1, 2) and (4, 3) is given by in equation

A tangent at a point on the circle x^{2}+y^{2}=a^{2 }intersects a concentric circle S at P and Q. The tangents to S at P and Q meet on the circle x^{2}+y^{2}=b^{2}. The equation to the circle S is