public static Line constructFromPointAndVector(Point A, double a, double b) {
Line l = new Line();
l.a = -b;
l.b = a;
l.A = A;
l.B = new Point(A.x + a, A.y + b);
l.c = b * A.x - a * A.y;
return l;
}
public static Line constructFromPointAndNormal(Point A, double a, double b) {
Line l = new Line();
l.a = a;
l.b = b;
l.A = A;
l.B = new Point(A.x - b, A.y + a);
l.c = -a * A.x - b * A.y;
return l;
}