2(sin(π/9-sin(8π/9))-3sin(8π/9) =
3cos(29π/18)+3(cos(29π/18)-cos(7π/18))
2*2sin((π/9-8π/9)/2)*cos((π/9+8π/9)/2)-3sin(8π/9) =
3cos(29π/18)+3 (-2)sin((29π/18+7π/18)/2)*cos((29π/18-7π/18)/2)
4*sin(-7π/18)*cos(π/2)-3sin(8π/9) =
3cos(29π/18)-6sin(π)*cos(11π/18)
4*sin(-7π/18)*0-3sin(8π/9) =
3cos(29π/18)-6*0*cos(11π/18)
-3sin(8π/9) =
3cos(29π/18)
-sin((9π-π)/9) = -sin(π-π/9) = -sin(π/9) = -sin(π/9) =
cos(18π+11π/18)) cos(π+11π/18) cos(11π/18) cos((9π+2π)/18)
-sin(π/9) = -sin(π/9) = -1
cos(π/2+π/9) sin(π/9)