theorem :: COMPTRIG:57

for x being Element of COMPLEX
for n being non zero Nat
for k being Nat holds ((n -root |.x.|) * (cos (((Arg x) + ((2 * PI) * k)) / n))) + (((n -root |.x.|) * (sin (((Arg x) + ((2 * PI) * k)) / n))) * <i>) is CRoot of n,x