题目

A(2,-4,-1),B(-1,5,1),C(3,-4,1),令a=,b=,则a+b对应的点为(    )A.(5,-9,2)        B.(-5,9,-2)             C.(5,9,-2)       D.(5,-9,2) 答案：答案:B解析: =(-1,0,-2), =(-4,9,0),∴a+b=(-5,9,-2).

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