向量OC=2/3向量OA+1/3向量OB则向量OC
问题描述：
向量OC=2/3向量OA+1/3向量OB则向量OC
A.AC=1/3AB B.AC=2/3AB C.AC=-1/3AB D.AC=-2/3AB
答
AC=OC-OA=2OA/3+OB/3-OA
=-OA/3+OB/3
=-(1/3)(OA-OB)
=(-1/3)BA
=AB/3
选A