>>247
-1+i = (√2) exp( (3/4)πi) の 3乗根は

(2^(1/6)) exp( (1/4) π i), (2^(1/6)) exp( (11/12) π i), (2^(1/6)) exp( -(5/12) π i)

√i = i^(1/2) = exp((1/2)πi)^(1/2) = exp((1/4)πi) or exp(-(3/4)πi)