设a=(1+√3i)/2,b=(1-√3i)/2,当n∈N*时,计算a^n+b^n用棣模佛公式a=1/2 +√3i/2=cos30°+isin30° b=(1-√3i)/2=cos330°+isin330°a^n+b^n=(cosn30°+isinn30°)+ cosn330°+isinn330°=(cosn30°+cosn330°)+i(sinn30°+sinn330°)=
