sinπ/18sin5π/18 sin（- 65π/18)=cos(π/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/...多谢了OK