5.3.1

        static int fact(int a)
        {
            int f = 1;
            for (int i = 1; i <= a; i++)
            {
                f *= i;
            }
            return f;
        }
        delegate double si(int i,double x);
        static double s1(int i,double x)
        {
            return Math.Cos(i * x) / fact(i);
        }
        static double s2(int i, double x)
        {
            return Math.Pow(-1, i) * Math.Cos(i * x) / (i * i);
        }
        static double summa(si s, double sum, int n,double x, double h)
        {
            for (int i = 1; i <= n; i++)
            {
                sum += s(i, x);
                x += h;
            }
            return sum;
        }
        static void Main(string[] args)
        {
            double sum1 = summa(s1, 1, 10, 0.1, 0.1);
            WriteLine();
            double sum2 = summa(s2, 0, 20, Math.PI / 5, Math.PI / 25);
        }