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| 1. |
Cos 20°.cos40°.cos80°=1/8 |
| Answer» 1/sin20*sin20.cos20.cos40.cos80.=. 1/2sin20*2sin40.cos40.cos80=. 1/4sin20*2sin80.cos80. 1/8sin20*2sin160=1/8sin20*sin(180-20). 1/8sin20*sin20=1/8 | |