Find the equation of the circle concentric with x2+y2−4x−6y−3=0 and which touches the y-axis.
Center of given circle = (42,62)=(2,3)
Let (x−2)2+(y−3)2=r2 be a concentric circle
Since x = 0 is a tangent
Radius = Perpendicular distance from center to tangent
⟹r=|2+0|√1+0⟹r=2
Equation of circle is (x−2)2+(y−3)2=22
⟹x2+y2−4x–6y+9=0