Equation (3.20) has the following form

solution of which is given as

Solution of equation (3.20) can be written as

                                                                                                      (3.21)

                        

Hence the general solution of equation (3.18) from equations (3.19) and (3.21) is given by the equation

                                                                                                                      (3.22)

where A and B are integration constants to be determined from initial conditions.