cos20°cos40°cos80°怎么算

2024-12-03 03:20:46
推荐回答(1个)
回答1:

原式=2sin20cos20cos40cos80/2sin20
=sin40cos40cos80/2sin20
=2sin40cos40cos80/4sin20
=sin80cos80/4sin20
=2sin80cos80/8sin20
=sin160/8sin20
=sin20/8sin20
=1/8