判断夹角大于100°

Question

A(x1,y1) B(x2,y2) C(x3,y3)  
判断AC与BC夹角是否大于100°

Answer 1

            int x1,x2,x3,y1,y2,y3;
            Vector v1 = new Vector(x1, y1);
            Vector v2 = new Vector(x2, y2);
            Vector v3 = new Vector(x3, y3);
            Vector v13 = v1 - v3;
            Vector v23 = v2 - v3;
            double angle = Vector.AngleBetween(v13, v13);
            if (Math.Abs(angle) > 100)
            {
                //todo
            }

Answer 2

不好意思,写错一句double angle = Vector.AngleBetween(v13, v23);