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设平面向量=(1,2),=(-2,y),若∥,则|3+|等于( ) A. B. ...
设平面向量
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=(1,2),
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=(-2,y),若
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∥
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,则|3
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+
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|等于( )
A.
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B.
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C.
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D.
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考点分析:
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