C#编程已知三个点求组成三角形的面积和周长

答案：举个例子，希望有所帮助。
代码
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace TestWork
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            double x1 = Convert.ToDouble(this.textBox1.Text);
            double y1 = Convert.ToDouble(this.textBox2.Text);
            double x2 = Convert.ToDouble(this.textBox3.Text);
            double y2 = Convert.ToDouble(this.textBox4.Text);
            double x3 = Convert.ToDouble(this.textBox5.Text);
            double y3 = Convert.ToDouble(this.textBox6.Text);
            double a = System.Math.Sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
            double b = System.Math.Sqrt((x2 - x3) * (x2 - x3) + (y2 - y3) * (y2 - y3));
            double c = System.Math.Sqrt((x1 - x3) * (x1 - x3) + (y1 - y3) * (y1 - y3));
            double L = a + b + c;
            double p = L / 2;
            double S = System.Math.Sqrt(p*(p - a)*(p - b)*(p - c));
            MessageBox.Show("三角形周长：" + L.ToString() + Environment.NewLine + "三角形面积：" + S.ToString(), "提示信息");                
        }
      
    }
}
结果
1行:INPUT   x1，y1   2行:INPUT   x2，y2  3行:x3，y3  4行:a=SQR[（x1-x2)^2+(y1-y2)^2]   5行:b=SQR[（x2-x3)^2+(y2-y3)^2]    6行:c=SQR[（x3-x1)^2+(y3-y1）^2]     7行:L=a+b+c     8行:P=L/2     9行:S=SQR[p(p-a)(p-b)(p-c)]    10行:PRINT  L，S  11行:END

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