若x=π12,则cos4x-sin4x的值为( ) A.0 B.12 C.22 D.32
问题描述:
若x=
,则cos4x-sin4x的值为( )π 12
A. 0
B.
1 2
C.
2
2
D.
3
2
答
cos4x-sin4x=(cos2x-sin2x)(cos2x+sin2x)
=cos2x-sin2x
=cos2x=cos(2×
)π 12
=cos
=π 6
3
2
故选D