public class PlaneCircle extends Circle {
	// new instance fields
	public double cx, cy;

	// new constructor, special syntax to invoke Circle() constructor
	public PlaneCircle( double r, double x, double y ) {
		super(r);
		this.cx = x;
		this.cy = y;
	}

	// new instance method, area() and circumference() are inherited
	public boolean isInside( double x, double y ) {
		double dx = x-cx, dy = y-cy;
		double distance = Math.sqrt( dx*dx + dy*dy );
		return (distance < r );
	}
}