Suppose that x = (-1 + i(3^1/2))/2 and y = (-1-i(3^1/2))/2. Which of the following statements is not correct?
(A) x^5 + y^5 = -1
(B) x^7+ y^7 = -1
(C) x^9+ y^9 = -1
(D) x^11 + y^11 -1
(E) x^13 + y^13 -1
x^3 + y^3 = 1
so x^n + y^n = -1 for all n≠3k (k = 1,2,3,...)
so, C