private void button1_Click(object sender, EventArgs e)
        {
            string[] strPoint=textBox1.Text.Split(',');
            double[] dPoint=new double[6];
            for(int i=0;i<strPoint.Length;i++)
                dPoint[i] = double.Parse(strPoint[i]);
            textBox2.Text = getAngle(dPoint).ToString();
        }

        double getAngle(double[] dPoint)  //6个double 依次为x1,y1,x2,y2,x3,y3
        {
            double s1, s2, s3,p,S;
             s1=Math.Sqrt(Math.Pow(dPoint[0]-dPoint[2],2)+Math.Pow(dPoint[1]-dPoint[3],2));
            s2=Math.Sqrt(Math.Pow(dPoint[4]-dPoint[2],2)+Math.Pow(dPoint[5]-dPoint[3],2));
            s3=Math.Sqrt(Math.Pow(dPoint[0]-dPoint[4],2)+Math.Pow(dPoint[1]-dPoint[5],2));
            p = (s1 + s2 + s3) / 2;
            S = Math.Sqrt(p * (p - s1) * (p - s2) * (p - s3));
            return Math.Round(180*Math.Asin(2 * S / (s1 * s2))/3.14,1);//保留1位小数
        }