private static double threePointsAngle(Point vertex,Point A,Point B){
  double b=pointsDistance(vertex,A);
  double c=pointsDistance(A,B);
  double a=pointsDistance(B,vertex);
  return Math.toDegrees(Math.acos((a * a + b * b - c * c) / (2 * a * b)));
}

private static double threePointsAngle ( Point vertex , Point A , Point B ) { double b = pointsDistance ( vertex , A ) ; double c = pointsDistance ( A , B ) ; double a = pointsDistance ( B , vertex ) ; return Math . toDegrees ( Math . acos ( ( a * a + b * b - c * c ) / ( 2 * a * b ) ) ) ; }
calculate the point a ' s angle of rectangle consist of point a , point b , point c ;
