double b;
const double PI = 3.14159265;
double result2;
Console.WriteLine("1/4 - 1/4(sin(5/2*PI - 8b)) = ...");
Console.WriteLine("Введите b");
b = Convert.ToDouble(Console.ReadLine());
result2 = 1 / 4 - (1 / 4 * Math.Sin((5 / 2 * PI) - (8 * b)));
result2 = Math.Round(result2, 3);
Console.WriteLine("1/4 - 1/4(sin(5/2*PI - 8b)) = " + result2);