code: function crossProductZ(pointA,  pointB,  pointC) {
      var bX = pointB.x;
      var bY = pointB.y;
      return ((pointC.x - bX) * (pointA.y - bY)) - ((pointC.y - bY) * (pointA.x - bX));
    }
docs: / <summary> Returns the z component of the cross product between vectors BC and BA.</summary>