Question

已知，，，點C在內， ，若=2m+m（），則=（    ）                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

A．1

B．2

C．

D．4

Answer 1

D

試題分析：根據題意，由于，，，點C在內， ，若=2m+m（），那么兩邊同時乘以,結合向量的夾角和模長公式，和數量積為零得到參數k的值為4，故選D.
點評：主要是考查了向量的數量積的運算，以及向量的垂直的充要條件的運用，屬于基礎題。