# Math Help - factorising indices

1. ## factorising indices

Am I right in saying you cannot factorise the expression x^n+1 where n if greater or equal to 3 is odd?

apart from x^3 which would be (x+1)(x^2-x+1)

2. Originally Posted by Mukilab
Am I right in saying you cannot factorise the expression x^n+1 where n if greater or equal to 3 is odd?

apart from x^3 which would be (x+1)(x^2-x+1)
$x^5 +1 = (x+1) (x^4-x^3+x^2-x+1)$

$x^7 +1 = (x+1) (x^6-x^5+x^4-x^3+x^2-x+1)$

$x^9 +1 = (x+1) (x^2-x+1) (x^6-x^3+1)$