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

=dfrac (alpha +1)(2).

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

若 |X|lt x =alpha , 则x等于 () .-|||-(A) zg/2 (B) _(1)-dfrac (a)(2) (C) dfrac (21-a

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

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

dfrac (Fx)(sin alpha ) D. dfrac (Fx)(cos alpha )

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

(B) =2, =dfrac (1)(3).-|||-(C) =1, =dfrac (1)(2). (D) =1, =-dfrac (1)(3),求指导本题解题

6.设α1,α2,α3线性无关, (beta )_(1)=a(alpha )_(1)+b(alpha )_(2) (beta )_(2)=a(alpha )_(

(B) dfrac (1)(2)(X)_(1)+dfrac (1)(2)(X)_(2)-|||-(C) dfrac (1)(2)(X)_(1)+dfrac (1