Consider the given circles. S1:x2+y2+4y−7=0 S2:2x2+2y2+3x+5y−9=0 And S3:x2+y2+y=0 The radical axis of circle S1 and S2 is x−y−1=0 The radical axis of circle S2 and S3 is x+y−3=0 Thus, the coordinate of radical centre is (2,1) and the radius is, r=√4+1+8−7 =√6 Hence, the equation of the required circle is, (x−2)2+(y−1)2=6 x2+y2−4x−2y−1=0