For a circle that passes through a point(a,band touches both axes, the center of the circle lies on the perpendicular bisector of the line segment formed by the point and the origin.
Given the point (4, -2), the midpoint of the segment joining (4, -2) and the origin (0, 0) is , where and .
Now, the radius () is the distance from the center to the given point (4, -2). Using the distance formula:
Therefore, the equation of the circle is: