multiple matrix

using System;

class Program {
    static double[,] matr3_mul(double[,] mas1, double[,] mas2)
        {
            double[,] res = new double[3, 3];
            for (int i=0; i<3; i++) //строки
            {
                for (int j=0; j<3; j++) //столбцы
                {
                    res[i, j] = mas1[i, 0] * mas2[0, j] + mas1[i, 1] * mas2[1, j] + mas1[i, 2] * mas2[2, j];
                }
            }
            return res;
        }
    static void Main(string[] args) {
        double[,] mas1={
            {5, 8, -4},
            {6, 9, -5},
            {4, 7, -3}
        };
        double[,] mas2={
            {3, 2, 5},
            {4, -1, 3},
            {9, 6, 5}
        };
    double[,] res=matr3_mul(mas1, mas2);
        for (int i=0; i<3; i++){
            for (int j=0; j<3; j++){
                Console.Write(res[i, j]+" ");
            }
        Console.WriteLine();
        }
    }
}