using System; using System.Numerics; namespace ConsoleApp1 { class Program { static void Main(string[] args) { Complex z = new Complex(1, 1); Complex acos_z = Complex.Acos(z); Console.WriteLine($"Acos({z}) = {acos_z}"); } } }In this example, we first create a complex number 'z' using the Complex class. We then use the Complex.Acos method to calculate the arccosine of 'z' and store it in the 'acos_z' variable. Finally, we print the result using the Console.WriteLine method. This function is part of the System.Numerics namespace, which is included in the .NET Framework Class Library.