若，且，则向量与的夹角为（    ）
Ａ．30⁰   B．60⁰    Ｃ．120⁰  Ｄ．150⁰

已知向量，,若，则的值为（    ）                                                 

A．

B．

C．

D．

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

A．1

B．2

C．

D．4

设、、为非零向量，且++=，向量、夹角为，，则向量与的夹角为     。

已知向量，若是等边三角形，则的面积为                   .

非零向量，，，若向量，则的最大值为（   ）

A．

B．

C．

D．以上均不对

已知以为直径的半圆，圆心为，为半圆上任意点，在线段上，则的最小值是（   ）

A．

B．

C．

D．

在△ABC中，，记，△ABC的面积为，且满足.
（1）求的取值范围；
（2）求函数的最大值和最小值.

已知向量，，若，则的最小值为             .

已知向量满足，满足，，若与共线，则的最小值为（    　）

A．

B．

C．

D．