Here, equation of tangent on C1 at (2,1) is: 2x+y−(x+2)−1=0 Or x+y=3 If it cuts off the chord of the circle C2 then the equation of the chord is: x+y=3 ∴ distance of the chord from (3,−2) is : d=23−2−3=2 Also, length of the chord is l=4 ∴ radius of C2=r=(2l)2+d2=(2)2+(2)2=6