If the circle x2+y2+6x−2y+k=0 bisects the circumference of the circle x2+y2+2x−6y−15=0, then k _______
-23
Equation of the common chord of the given circles is
4x+4y+k+15=0. . . .(1)
Since x2+y2+6x−2y+k=0 bisects the circumference of x2+y2+2x−6y=15
∴ (1) is the diameter of x2+y2+2x−6y=15
⇒4(−1)+4(3)+k+15=0 ⇒k=−23