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单选题
难度系数:

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1IDxiPm08L2I+PGltZyB3aWR0aD0zIGhlaWdodD0yMSBzcmM9Imh0dHBzOi8vcDEucWluZ2d1by5jb20vRzEvTTAwL0FGLzk5L3JCQUNGRk5IcG9LalhuYlFBQUFBdGd1NmEtYzUwNC5wbmciPjxiPm48L2I+PXw8Yj5tPC9iPnx8PGI+bjwvYj58PGltZyB3aWR0aD0xNiBoZWlnaHQ9NDIgc3JjPSJodHRwczovL3AyLnFpbmdndW8uY29tL0cxL00wMC9BRi85OS9yQkFDRkZOSHBvU3o0N0FkQUFBQkgzcmdKS2c0MzUucG5nIj4=
  • 提示2IDI8aW1nIHdpZHRoPTM2IGhlaWdodD0yMSBzcmM9Imh0dHBzOi8vcDIucWluZ2d1by5jb20vRzEvTTAwL0FGLzlBL3JCQUNGRk5IcG9XVGhiMmlBQUFCZ2hOMmtFUTgzNS5wbmciPitjb3NCLTE9MA==