cos75°cos15°-sin255°sin165°的值是(  ) A.12 B.−12 C.32 D.0

问题描述:

cos75°cos15°-sin255°sin165°的值是(  )
A.

1
2

B.
1
2

C.
3
2

D. 0

cos75°cos15°-sin255°sin165°
=cos75°cos15°-sin(180°+75°)sin(180°-15°)
=cos75°cos15°+sin75°sin15°
=cos(75°-15°)
=cos60°
=

1
2

故选A