using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string stringToCheck = "text1text2text3";

        string[] stringArray = { "text1", "someothertext"};

​

        if(stringArray.Any(a=> String.Equals(a, stringToCheck, StringComparison.InvariantCultureIgnoreCase)) )

        { 

            Console.WriteLine(true);

        }

        else

        {

            Console.WriteLine(false);

        }

        //IndexOf

        if (stringArray.Any(w=> w.IndexOf(stringToCheck, StringComparison.InvariantCultureIgnoreCase)>=0))

        { 

            Console.WriteLine(true);

        }

        else

        {

            Console.WriteLine(false);

        }

    }

}