答案:必要.
a//b未必有a=b,比如a=1,b=2.
a=b一定有a//b.因为对任意非零向量a有a//a.
设向量|a|·|b|≠0,则向量a//b是向量a=b的______条件.
设向量|a|·|b|≠0,则向量a//b是向量a=b的______条件.
数学人气：999 ℃时间：2020-02-05 18:29:33
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