Z = sin2kpi/11 + icos2kpi/11

Z = Ae^i@                    (ellulers form)

A = (sin²@+cos²@)^1/2 = 1 ,

@ = 2kpi/11

Z = e^i(2kpi/11) 

sigma Z  = sigma e^i(2kpi/11)   lim k=1 to k=10

            =e^{i[2pi/11 (1+2+3........10)]  (AP series)}                         [ sum of Ap is n/2(2a+(n-1)d]

           =e^{i[2pi/11(55)]}

           =e^i10pi = cos10pi + isin10pi = 1