求值：cos12°cos24°cos48°cos96°

cos12°cos24°cos48°cos96°
=2sin12°cos12°cos24°cos48°cos96°/2sin12°
=sin24°cos24°cos48°cos96°/2sin12°
=2sin24°cos24°cos48°cos96°/4sin12°
=sin48°cos48°cos96°/4sin12°
=2sin48°cos48°cos96°/8sin12°
=sin96°cos96°/8sin12° sin96°=cos6° cos96°=sin6°
=2sin6°cos6°/16sin12°
=sin12°°/16sin12°
=1、16

12的和48的，12的和96的积化和差然后cos72°和cos36°是可以画一个底角是72°的等腰三角形算出来的...