Объединение в одну коллекцию

using System;
using System.Collections.Generic;

internal class Program
{
    static void Main(string[] args)
    {
        string[] numbers = { "1", "4", "6", "1", "2", "12", "9", "7" };
        string[] numbers2 = { "3", "3", "2", "5", "8", "1", "4", "2" };

        List<string> combinedNumbers = new List<string>();

        AddNumbersToList(combinedNumbers, numbers);
        AddNumbersToList(combinedNumbers, numbers2);

        foreach (string number in combinedNumbers)
        {
            Console.Write(number + " ");
        }

        Console.ReadKey();
    }

    static void AddNumbersToList(List<string> finalNumbers, string[] elementaryNumbers)
    {
        foreach (string number in elementaryNumbers)
        {
            if (finalNumbers.Contains(number) == false)
            {
                finalNumbers.Add(number);
            }
        }
    }
}