Which of the following is NOT a true statement ? O A For a given ay" +by' + cy=de++lcosx where a brc and d are constants method of undetermined coefficients is applicable O B) Every differential equation can be solved by the method of power series. OC) Some functions do not have the Laplace transform. OD Method of power series solution can solve ay" +by'+cy=0 where a, b and c are constants. O E)Method of variation of parameters can work for any differential equations if the complementary solution is already known.