The locus of the centre of the circle which bisects the circumferences of the circles x2+y2=4 & x2+y2−2x+6y+1=0 is
If a circle passes through the point (1, 2) and cuts the circle x2+y2=4 orthogonally, then the equation of the locus of its centre is
Locus of the centre of the circle which touches the two circle x2+y2+8x–9=0 and x2+y2–8x+7=0 externally, is
If the circle x2+y2+6x−2y+k=0 bisects the circumference of the circle x2+y2+2x−6y−15=0, then k _______