(a－b＋c)的平方怎么计算

(a-b+c)²
=(a+c-b)²
=(a＋c)²-2b(a+c)+b²
=a²+2ac+c²-2ab-2bc+b²
=a²+b²+c²-2ab-2bc+2ac

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

namespace WindowsFormsApplication4

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            double a, b, c,X,y;

            a = Convert.ToInt32(textBox1.Text);

            b = Convert.ToInt32(textBox2.Text);

            c = Convert.ToInt32(textBox3.Text);

            X = a - b - c;

            y = Math.Pow(X, 2);

            MessageBox.Show("y="+y);

        }

    }

}   照样子见一个窗体，输入代码！

先把a-b看到一个整体，如下：
[(a-b)+c]^2=(a-b)^2+2(a-b)*c+c^2

(a-b+c)^2 = a^2 + b^2 + c^2 - 2ab - 2bc + 2ac

直接去括号呗！