如果不趕時間可以自己推算出算式或者直接參考另一個博主的文章：
https://blog.csdn.net/liyuanbhu/article/details/52891868#commentBox
程序完整部分《C#已知三點求圓方程算法.rar》已經上傳到CSDN，地址是：
https://download.csdn.net/download/weixin_42117950/10903015
在這裏貼出算法部分：
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 DrawCircle
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
FirstPoint = new List<double>();
SecondPoint = new List<double>();
ThridPoint = new List<double>();
this.StartPosition = FormStartPosition.CenterScreen;//窗口居中
}
List<double> FirstPoint;
List<double> SecondPoint;
List<double> ThridPoint;
private void btn_Calculate_Click(object sender, EventArgs e)
{
//先清除上一次儲存的數值
FirstPoint.Clear();
SecondPoint.Clear();
ThridPoint.Clear();
//把文本框的數值加入到數組中
try
{
//第一點的X Y座標值
FirstPoint.Add(double.Parse(tb_FirstPointX.Text));
FirstPoint.Add(double.Parse(tb_FirstPointY.Text));
//第二點的X Y座標值
SecondPoint.Add(double.Parse(tb_SecondPointX.Text));
SecondPoint.Add(double.Parse(tb_SecondPointY.Text));
//第三點的X Y座標值
ThridPoint.Add(double.Parse(tb_ThirdPointX.Text));
ThridPoint.Add(double.Parse(tb_ThirdPointY.Text));
}
catch(Exception ex)
{
MessageBox.Show(ex.Message+"\n請重新輸入","提示",MessageBoxButtons.OK,MessageBoxIcon.Error);
return;
}
//算法內容
double a = FirstPoint[0] - SecondPoint[0];// X1-X2
double b = FirstPoint[1] - SecondPoint[1];//Y1-Y2
double c = FirstPoint[0] - ThridPoint[0];//X1-X3
double d = FirstPoint[1] - ThridPoint[1];//Y1-Y3
double aa = Math.Pow(FirstPoint[0], 2) - Math.Pow(SecondPoint[0], 2);//X1^2-X2^2
double bb = Math.Pow(SecondPoint[1], 2) - Math.Pow(FirstPoint[1], 2);//Y2^2-Y1^2
double cc = Math.Pow(FirstPoint[0], 2) - Math.Pow(ThridPoint[0], 2);//X1^2-X3^2
double dd = Math.Pow(ThridPoint[1], 2) - Math.Pow(FirstPoint[1], 2);//Y3^2-Y1^2
double E = (aa-bb) / 2;
double F = (cc-dd) / 2;
double resultY = (a * F - c * E) / (a * d - b * c);
double resultX = (F * b - E * d) / (b * c - a * d);
double resultR = Math.Sqrt((Math.Pow((FirstPoint[0] - resultX), 2)) + (Math.Pow((FirstPoint[1] - resultY), 2)));
//輸出圓心的座標和半徑值
lb_Point.Text = "X座標爲：" + resultX.ToString() + "; Y座標爲：" + resultY.ToString();
lb_Radius.Text = resultR.ToString();
}
}
}