cos40度乘以cos80度乘以cos160度 .
问题描述:
cos40度乘以cos80度乘以cos160度 .
答
cos40cos80cos160
=sin40cos40cos80cos160/sin40
=1/2sin80cos80cos160/sin40
=1/4sin160cos160/sin40
=1/8sin320/sin40
=1/8sin(360-320)/sin40
=1/8