UravnSystem/FunctionSystem/Level1.cs

//#define IsTestDownLevel1
#define IsDriverUpperCos

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

namespace FunctionSystem
{
    public static class Level1
    {
#if IsTestDownLevel1

        #region заглушки
        public static double Cos(double x) => 1;
        #endregion

#elif IsDriverUpperCos

        #region
        public static double Cos(double x)
        {
            Console.WriteLine($"Sin - {Level0.Sin(x)}");
            return 0;
        }
        #endregion

#else

        public static double Cos(double x)
        {
            x = ((x / (2 * Math.PI)) - Math.Truncate((x / (2 * Math.PI)))) * Math.PI * 2;
            if (x > Math.PI / 2 && x < Math.PI * 3 / 2)
            {
                return -(Math.Sqrt(1 - Math.Pow(Level0.Sin(x), 2)));
            }
            return Math.Sqrt(1 - Math.Pow(Level0.Sin(x), 2));
        }

#endif
    }
}