Sample of extension methods for matrix

Extensions.cs

using System;
using System.Linq;

namespace extension
{
    class Program
    {
        static void Main(string[] args)
        {
            double[][] matrix =
            {
                new double[] {5, 5, 5, 5, 5},
                new double[] {5, 5, 5, 5, 5},
                new double[] {5, 5, 5, 5, 5},
                new double[] {5, 5, 5, 5, 5},
                new double[] {5, 5, 5, 5, 5}
            };
            matrix.Print();
            matrix.ForEach(x => x + 5);
            matrix.Print();
            Console.ReadLine();
        }
    }

    internal static class Extensions
    {
        public static void ForEach(this double[][] matrix, Func<double, double> func)
        {
            for (var i = 0; i < matrix.Length; i++)
            {
                 matrix[i]= matrix[i].Select(func).ToArray();
            }
        }

        public static void Print(this double[][] matrix)
        {
            foreach (var d in matrix)
            {
                Console.WriteLine(string.Join("\t", d));
            }
        }
    }
}