1.若x=π/2,则cos^2x-sin^2x的值等于( )A.1/4 B.1/2 C.√2/2 D.√3/22.已知tanx=3/4,则tan2x=( )A.-7/24 B.7/24 C/-24/7 D.24/73.cos75°sin75°的值为( )A.1/4 B.1/2 C√2/2 D.√3/24.已知sin2θ=12/13,π

1.若x=π/2,则cos^2x-sin^2x的值等于( )A.1/4 B.1/2 C.√2/2 D.√3/22.已知tanx=3/4,则tan2x=( )A.-7/24 B.7/24 C/-24/7 D.24/73.cos75°sin75°的值为( )A.1/4 B.1/2 C√2/2 D.√3/24.已知sin2θ=12/13,π
1.若x=π/2,则cos^2x-sin^2x的值等于( )
A.1/4 B.1/2 C.√2/2 D.√3/2
2.已知tanx=3/4,则tan2x=( )
A.-7/24 B.7/24 C/-24/7 D.24/7
3.cos75°sin75°的值为( )
A.1/4 B.1/2 C√2/2 D.√3/2
4.已知sin2θ=12/13,π

1.若x=π/2,则cos^2x-sin^2x的值等于( )A.1/4 B.1/2 C.√2/2 D.√3/22.已知tanx=3/4,则tan2x=( )A.-7/24 B.7/24 C/-24/7 D.24/73.cos75°sin75°的值为( )A.1/4 B.1/2 C√2/2 D.√3/24.已知sin2θ=12/13,π
cos^2x-sin^2x=cos2x=-1
第一题无答案
2.D
3.A
4.
sin2θ=12/13,π<θ<5π/4,则cos2θ=5/13
sin4θ=2sin2θcos2θ=120/169
cos4θ=(cos2θ）^2-(sin2θ)^2=-119/169
tan4θ=sin4θ/cos4θ=-120/119
5.D

悬赏太低了