If xr=cos(π3r)+isin(π3r), then x1x2x3.......to∞is:
1
-1
i
-i
(cosα+isinα)(cosβ+isinβ)=cos(α+β)+isin(α+β)
x1x2x3......=cis(π3(11−13))=cisπ2=i