化简cos40°cos25°1-sin40°=(  ) A.1 B.3 C.2 D.2

问题描述:

化简

cos40°
cos25°
1-sin40°
=(  )
A. 1
B.
3

C.
2

D. 2

原式=

cos220°-sin220°
cos25°
(cos20°-sin20°)2
=
cos20°+sin20°
cos25°
=
2
cos(45°-20°)
cos25°
=
2

故选:C.