色药轱辘白粥
幼苗
共回答了21个问题采纳率:85.7% 举报
a=(cos23度,cos67度)=(cos23度,sin23度),
b=(cos68度,cos22度)=(cos68度,sin68度),
a*b =cos23*cos68+sin23*sin68
=cos(68-23)=cos45=√2/2
(2) |a|=|b|=1,a*b=√2/2
|u|^2=|a+tb|^2=(a+tb)^2=a^2+2ta*b+t^2*b^2
=t^2+√2t+1
=(t+√2/2)^2+1/2
故当t=-√2/2时,|u|最小值是√2/2
1年前
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