1.设向量a=(cos23度,cos67度),b=(cos68度,cos22度),u=a+tb,t属于R
问题描述:
1.设向量a=(cos23度,cos67度),b=(cos68度,cos22度),u=a+tb,t属于R
(1),求a*b
(2),求u的模的最小值
答
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+...