A circle passes through the focus of parabola x2=4y . If the circle touches the parabola at  (6,9), then square of its radius is

Equation of tangent to parabola x2 = 4y at point P(6,9) is: 6x=2(y+9) or 3x−y−9=0Equation of family of circles touching tangent at point P is: (x−6)2+(y−9)2+λ(3x−y−9)=0Circle passes through the point (0,1) =focus of the parabola. ∴λ=10Thus, the equation of circle is:x2+y2+18x−28y+27=0 Radius of the circle is 510 .