已知|a|=1,|b|=2。(1)若a//b,求a·b; (2)若a、b的夹角为60°,求|a+b|; (3)若a-b与a垂直,求当k为何值时,(...

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问题 已知|a|=1,|b|=2。(1)若a//b,求a·b; (2)若a、b的夹角为60°,求|a+b|; (3)若a-b与a垂直,求当k为何值时,(ka-b)⊥(a+2b)。
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