z^3=√343[cos(pai-arctan9√3/10+isin(pai-arctan9√3/10)],z=√7{cos[(pai-arctan9√3/10+2npai)/3]+isin[(pai-arctan9√3/10+2npai)/3]},z*z共轭=7，z+z共轭=2√7cos[(pai-arctan9√3/10
