cos12°cos24°cos48°cos84°=

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cos12°cos24°cos48°cos84°=

cos12°cos24°cos48°cos84°=
cos12°cos24°cos48°cos84°=

cos12°cos24°cos48°cos84°=
cos12°cos24°cos48°cos84°
=16sin12cos12°cos24°cos48°cos84°/16sin12
=8sin24cos24cos48cos84/16sin12
=4sin48cos48cos84/16sin12
=2sin96cos84/16sin12
因为sin96=cos6
cos84=sin6
=2sin6cos6/16sin12
=sin12/16sin12
=1/16

用倍角公式,自己尝试就可以做出来了,自己求出来,这样下次就更有印象!

cos12°cos24°cos48°cos84°
=sin12°cos12°cos24°cos48 cos84°/sin12° =sin24°cos24°cos48°cos84°/2sin12°
=sin48°cos48° cos84°/4sin12°
=sin96°cos84°/8sin12°
= sin84°cos84°/8sin12°
=sin168°/16sin12°
=sin12°/16sin12°
=1/16

这是何意?要求做什么?