设alpha =(dfrac (1)(2),0,0,dfrac (1)(2)) ,=E-(alpha )^Talpha =E+2(alpha )^Talpha ,则AB=( )alpha =(dfrac (1)(2),0,0,dfrac (1)(2)) ,=E-(alpha )^Talpha =E+2(alpha )^Talpha ,

(B) alpha lt dfrac (1)(2). (C) alpha geqslant dfrac (1)(2), (D) alpha gt dfrac (

例1(1)(2021·全国甲卷)若 alpha in (0,dfrac (pi )(2)), tan2α-|||-=dfrac (cos alpha )(2-s

=dfrac (alpha +1)(2).

设矩阵 =((alpha )_(1),(alpha )_(2),(alpha )_(3),(beta )_(1))，=((alpha )_(1),(alpha

向量方程((a)_(1)+alpha )-7((alpha )_(2)+alpha )+4(alpha )_(3)=0，其中((a)_(1)+alpha )-7

[题目]若 sin alpha =dfrac (1)(3), 则 cos 2alpha = ()()-|||-

设向量(alpha )_(1)=((1,1,-1))^T (alpha )_(2)=((0,2,1))^T,(alpha )_(1)=((1,1,-1))^T

对于向量组alpha_1,alpha_2,ldots,alpha_m，若0alpha_1+0alpha_2+ldots+0alpha_m=0，则该向量组()。A

14.设 (alpha )_(1)=(1,-1,2,4) (alpha )_(2)=(0,3,1,2), (alpha )_(3)=(3,0,7,14), (a

【题目】-|||-设α1,a2,α3线性无关,证明: (alpha )_(1)+(alpha )_(2), (alpha )_(2)+(alpha )_(3),