QuadraticEquation

class QuadraticEquation
    {
        static void Main(string[] args)
        {
            double a, b, c;
            Console.WriteLine("ax^2 + bx + c = 0");
            Console.WriteLine("");
            Console.Write("Enter a: ");
            bool aIsValid = double.TryParse(Console.ReadLine(), out a);
            Console.Write("Enter b: ");
            bool bIsValid = double.TryParse(Console.ReadLine(), out b);
            Console.Write("Enter c: ");
            bool cIsValid = double.TryParse(Console.ReadLine(), out c);

            if (aIsValid && bIsValid && cIsValid)
            {
                //D = b^2 - 4*a*c
                double d = b * b - (4 * a * c);
                double x1 = (-b + Math.Sqrt(d)) / (2 * a);
                double x2 = (-b - Math.Sqrt(d)) / (2 * a);
                if (double.IsNaN(x1) && double.IsNaN(x2))
                {
                    Console.WriteLine("No real roots.");
                }
                else
                {
                    Console.WriteLine("{0} {1}", x1, x2);
                }
            }
            else
            {
                Console.WriteLine("Please enter valid data.");
                Console.Beep();
            }
        }
    }