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
答
原式=
=cos220°-sin220° cos25°
(cos20°-sin20°)2
=cos20°+sin20° cos25°
=
cos(45°-20°)
2
cos25°
,
2
故选:C.