Question

设单位向量e1,e2夹角是60,a=e1+e2,b=e1+te2,若a,b夹角是锐角,求t取值范围

Answer 1

∈（0,π/2)cos=[ab]/|a|*|b|>0

ab>0

(e1+e2)(e1+te2)>0

e1^2+(t+1)e1e2+te2^2>0

1+(t+1)/2+t.>0==>t>-1