若A ( 2, -4, -1 ),B(-1,5,1),C(3,-4,1),令a=,b=,则a+ b对应的坐标为
A.(-5,9,-2) | B.(-5,-9,-2) |
C.(-5,-9,2) | D.(5,-9,-2) |
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若A ( 2, -4, -1 ),B(-1,5,1),C(3,-4,1),令a=,b=,则a+ b对应的坐标为
A.(-5,9,-2) | B.(-5,-9,-2) |
C.(-5,-9,2) | D.(5,-9,-2) |
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