public Line getLine(Point a, Point b) {
		if (isEqual(a.getX(), b.getX()) && isEqual (a.getY(), b.getY())) {
			return null;//two points are the same
		}
		else if (isEqual(a.getX(), b.getX())) {
			return null;//the line is vertical
		}
		else {
			double k = (b.getY() - a.getY())/(b.getX() - a.getX());
			double delta = b.getY() - b.getX() * k;
			Line line1 = new Line(k, delta);
			return line1;
		}
	}