已知，，，点C在内， ，若=2m+m（），则=（    ）                                                   

题型：不详难度：来源：

已知，，，点C在内， ，若=2m+m（），则=（    ）                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

A．1

B．2

C．

D．4

答案

D

解析

试题分析：根据题意，由于，，，点C在内， ，若=2m+m（），那么两边同时乘以,结合向量的夹角和模长公式，和数量积为零得到参数k的值为4，故选D.
点评：主要是考查了向量的数量积的运算，以及向量的垂直的充要条件的运用，属于基础题。