Question

数学三角函数高中 sinπ/18sin5π/18 sin（- 65π/18 sin之间为乘法

数学三角函数高中 sinπ/18sin5π/18 sin（- 65π/18
sin之间为乘法

Answer 1

sinπ/18sin5π/18 sin（- 65π/18)

=cos(π/配枯坦2-π/18)*cos(π/2-5π/18) sin（- 72π/18+7π/18)
=cos(4π/9)cos(2π/9)*sin(7π/18)
=cos(2π/9)*cos(4π/9)cos(π/2-7π/18)
=cos(π/9)*cos(2π/9)cos(4π/9)
=2sin(π/9)cos(π/9)*cos(2π/9)cos(4π/9)/[2sin(π/9)]
=2sin(2π/9)*cos(2π/败宴9)cos(4π/9)/[4sin(π/9)]
=2sin(4π/9)*cos(4π/9)/[8sin(π/9)]
=sin(8π/9)/培桐[8sin(π/9)]
=sin(π/9)/[8sin(π/9)]
=1/8

追问

多谢了

追答

OK