一元三次方程求解 c#

在 C# 中，可以使用以下代码来求解一元三次方程：

using System;

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("请输入一元三次方程的系数：");
        Console.Write("a = ");
        double a = Convert.ToDouble(Console.ReadLine());

        Console.Write("b = ");
        double b = Convert.ToDouble(Console.ReadLine());

        Console.Write("c = ");
        double c = Convert.ToDouble(Console.ReadLine());

        Console.Write("d = ");
        double d = Convert.ToDouble(Console.ReadLine());

        double discriminant = Math.Pow(b, 2) - 3 * a * c;
        double delta = (2 * Math.Pow(b, 3) - 9 * a * b * c + 27 * Math.Pow(a, 2) * d) / (2 * Math.Sqrt(Math.Pow(b, 2) - 3 * a * c));

        if (discriminant > 0)
        {
            double theta = Math.Acos(delta) / 3;
            double x1 = -2 * Math.Sqrt(discriminant) * Math.Cos(theta) - b / (3 * a);
            double x2 = -2 * Math.Sqrt(discriminant) * Math.Cos(theta + (2 * Math.PI / 3)) - b / (3 * a);
            double x3 = -2 * Math.Sqrt(discriminant) * Math.Cos(theta - (2 * Math.PI / 3)) - b / (3 * a);

            Console.WriteLine("方程的根为：");
            Console.WriteLine("x1 = " + x1);
            Console.WriteLine("x2 = " + x2);
            Console.WriteLine("x3 = " + x3);
        }
        else if (discriminant == 0)
        {
            double x1 = -2 * Math.Pow(delta, 1 / 3) - b / (3 * a);
            double x2 = Math.Pow(delta, 1 / 3) - b / (3 * a);

            Console.WriteLine("方程的根为：");
            Console.WriteLine("x1 = " + x1);
            Console.WriteLine("x2 = " + x2);
        }
        else
        {
            double r = Math.Sqrt(Math.Pow(delta, 2) - Math.Pow(discriminant, 3));
            double phi = Math.Acos(-delta / Math.Sqrt(Math.Pow(delta, 2) - Math.Pow(discriminant, 3))) / 3;
            double x1 = 2 * Math.Sqrt(discriminant) * Math.Cos(phi) - b / (3 * a);
            double x2 = 2 * Math.Sqrt(discriminant) * Math.Cos(phi + (2 * Math.PI / 3)) - b / (3 * a);
            double x3 = 2 * Math.Sqrt(discriminant) * Math.Cos(phi - (2 * Math.PI / 3)) - b / (3 * a);

            Console.WriteLine("方程的根为：");
            Console.WriteLine("x1 = " + x1);
            Console.WriteLine("x2 = " + x2);
            Console.WriteLine("x3 = " + x3);
        }
    }
}

在运行程序时，会提示输入一元三次方程的系数 a、b、c 和 d，然后会输出方程的根。请注意，这段代码仅适用于实数根的情况，对于复数根的情况需要进行额外处理。