Let p(x) = xn + an
The zero of x + a is - a. | x + a = 0 ⇒ x = - a
Now,
p(- a) = (- a)n + an = (- 1)nan + an
     = (- 1)an + anÂ
  Â
 n is an odd positive interger
  (-1)n = - 1
= - an + an = 0
∴ By Factor Theorem, x + a is a factor of xn + an for any odd positive integer n.