（易线性表示）设a，b是两个不共线的非零向量，若向量ka+2b与8a+kb的方向相反，则k=______．
题型：不详难度：来源：
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答案
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∴k=8t，2=kt，得t=-
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∴k=-4．
故答案为：-4
举一反三
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题型：b|；⑤若|a|=1，则a=±1．其中假命题的个数为______．
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