def write_matrix
      array = Array.new
      @left_system_of_equations.keys.each do |key|
        array << @left_system_of_equations[key]
      end
      @right_system_of_equations.keys.each do |key|
        array  <<  @right_system_of_equations[key]
      end
       @array << array
    end
def write_matrix
      array = Array.new
      @left_system_of_equations.keys.each do |key|
        array << @left_system_of_equations[key]
      end
      @right_system_of_equations.keys.each do |key|
        array  <<  @right_system_of_equations[key]
      end
       @array << array
    end
3. Rearrange the system of equations and write it in a matrix
   a   b   c  d
O  0   2  -2  -1
 [[0,2,-2,-1]]