int n = 1;
double x = 1.0, h = 1.0;double deriv = Math.Cos(x), diffquo, error;
Console.WriteLine(deriv);
while(n <= 20) {
h = h / 10;
diffquo = (Math.Sin(x + h) - Math.Sin(x)) / h; /* производная */
error = Math.Abs(deriv - diffquo);
//Console.WriteLine("h={0},diff={1}, error={2}",h, diffquo, error);
Console.WriteLine(error);
n++;
}