几个余弦相乘怎么算?cosπ⼀9 cos2π⼀ 9cos3π⼀9 cos4π⼀9.相乘怎么算?我是高中生马上要高考,今天考...

2025-06-22 16:49:52
推荐回答(2个)
回答1:

cosπ/9 cos2π/ 9cos3π/9 cos4π/9.
=(sinπ/9cosπ/9 cos2π/ 9cos3π/9 cos4π/9.)/sinπ/9
=(1/2sin2π/9cos2π/ 9cos3π/9 cos4π/9)/sinπ/9
=(1/8sin8π/9cos3π/9)/sinπ/9
=1/8*cos3π/9
=1/16

回答2:

你直接算不就得了