原式=-cos2π/3[-sin3π/5-icos3π/5]
=1/2*[-cosπ/10+isinπ/10]
=1/2*(cos9π/10+isin9π/10)π/10如何求得的cosx=sin(π/2-x)sinx=cos(π/2-x)cos2π/3去那了=-1/2cos9π/10如何来的你没学过三角函数啊那就算了，别问了