(tan10°−3)sin40°=_．
问题描述：
(tan10°−
)sin40°=______．
3
答
(tan10°−
)sin40°
3
=(
−sin10° cos10°
)sin40°
3
=
×sin40°sin10°−
cos10°
3
cos10°
=2
×sin40°
sin10°− 1 2
cos10°
3
2 cos10°
=2
×sin40°sin(10°− 60°) cos10°
=
×sin40°−2sin50° cos10°
=
−sin80° cos10°
=-1．
故答案为：-1．