using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            double a, b, c,X1,X2;  //定义变量
            Console.WriteLine("--------求一元二次方程：ax^2+bx+c=0 --------");
            Console.WriteLine("请输入一个值给a：");
            a = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("请输入一个值给b：");
            b = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine("请输入一个值给c：");
            c = Convert.ToDouble(Console.ReadLine());
            X1=(-b+Math.Sqrt(b*b-4*a*c))/2*a;
            X2 = (-b - Math.Sqrt(b * b - 4 * a * c)) / 2 * a;
            if (b * b - 4 * a * c < 0) Console.WriteLine("此方程无实数解！");
            else if (b * b - 4 * a * c == 0) Console.WriteLine("只有一个解！X1=X2={0}",X2=X1);
            else
            Console.WriteLine("X1的值为：{0}\tX的值为：{1}", X2, X2);
            Console.ReadKey();
        }
    }
}

求一元二次方程