挑战习题
1/3单选题
难度:

1.已知ABC,向量m=(,1-)与n=(2,0)的夹角的余弦值为,则角B的大小为()
A
B
C
D
提示1:
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提示2:
IDI8aW1nIHdpZHRoPTM2IGhlaWdodD0yMSBzcmM9Imh0dHBzOi8vcDIucWluZ2d1by5jb20vRzEvTTAwL0FGLzlBL3JCQUNGRk5IcG9XVGhiMmlBQUFCZ2hOMmtFUTgzNS5wbmciPitjb3NCLTE9MA==
正确答案:Qw==
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