using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var array1 = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

        var array2 = new int[] { 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };

​

        var resultInner = array1.Where(p => array2.Any(a => a == p)).ToArray();

        var resultLeft = array1;

​

        PrintResult<int>(resultInner);

        PrintResult<int>(resultLeft);

​

    }

​

    public static void PrintResult<T>(T[] array) => Console.WriteLine(String.Join(", ", array));

}