三次根号下-27 等于多少?

三次根号下-27 等于多少?
在实数范围内,(-27)^(1/3)=-3；
在复数范围内-27=27(cosπ+isinπ)
故(-27)^(1/3)=3{cos[(π+2kπ)/3]+isin[(π+2kπ)/3]},k=0,1,2.
当k=0时,(-27)^(1/3)=3[cos(π/3)+isin(π/3)]=3(1/2+i√3/2)
当k=1时,(-27)^(1/3)=3(cosπ+isinπ)=-3
当k=2时,(-27)^(1/3)=3[cos(5π/3)+isin(5π/3)]=3[cos(π/3)-isin(π/3)]=3(1/2-i√3/2)