“…Remark: In [5,[33][34][35][36][37], the solutions "G" of the auxiliary equation are directly obtained according to the method of solving the second ordinary differential equation, and by the expression of G, the authors obtained the expression of G G . In [33][34][35][36][37], there are only two kinds of solutions G corresponding to the discriminant of the second ordinary differential equation which is larger than zero and less than zero, respectively; and in [5], the authors obtain three kinds of solutions corresponding to the discriminant of the second ordinary differential equation which is larger than zero, equal to zero and less than zero, respectively. However, it is difficult to solve the second order ordinary differential equation, sometimes it cannot get the simple expression of its solution or cannot obtain its solutions.…”