若x=π12,则cos4x-sin4x的值为(  ) A.0 B.12 C.22 D.32

问题描述:

x=

π
12
,则cos4x-sin4x的值为(  )
A. 0
B.
1
2

C.
2
2

D.
3
2

cos4x-sin4x=(cos2x-sin2x)(cos2x+sin2x)
=cos2x-sin2x
=cos2x=cos(2×

π
12

=cos
π
6
=
3
2

故选D