第一个就是三角形式啊
3(cos11π/6+isin11π/6)
sin3π/5-icos3π/5
=cos(3π/2+3π/5)+isin(3π/2+3π/5)
=cos(21π/10)+isin(21π/10)
=cos(π/10)+isin(π/10)