幻想Sherlock‧Holmes

若x²-13x+1=0,則x2+1/x²=       {推甄}

(A)167

(B)169

(C)171

(D)173

                                                                      ANS:(A)

                                                                                   (x+1/x)²=x²+2+1/x²

                                                                                           13²=x²+1/x²+2

                                                                                     x²+1/x²=196-2

                                                                                     x²+1/x²=167