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已知向量a=(x-1,2),b=(2,1),则a⊥b的充要条件是
A.x=- B.x-1 C.x=5 D.x=0
【解析】有向量垂直的充要条件得2(x-1)+2=0,所以x=0.D正确.
A.A1A2+B1B2=0 B.A1A2-B1B2=0 C.=-1 D.=1
两条直线A1x+B1y+C1=0,A2x+B2y+C2=0垂直的充要条件是
A.A1A2+B1B2=0 B.A1A2-B1B2=0
C.=-1 D.=-1