Circle

We have the circle S
S=x2+y2+2gx+4y+1=0
and the second circle be S1,
S1=x2+y2−2x−3=0
∵ Centre (1,0) and radius =2
Now, common chord of circles S and S1 is
‌S−S1=0
‌(2g+2)x+4y+4=0
If a circle bisects the circumference of another circle, then common chord is a diameter of the second circle.
‌2g+2+4=0⇒g=−3
∵‌‌S=x2+y2−6x+4y+1=0
Centre (3,−2)
Radius =√9+4−1=√12