题目内容

已知
(1)求的值
(2)若,其中O是原点,且的夹角。
(1)(2)

(1)                                …………2分
                                       …………4分
                                                                                    …………5分
(2)                                                                      …………7分
                                              …………9分
                                                                 …………10分
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