# factorising indices

• Sep 8th 2010, 11:34 AM
Mukilab
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)
• Sep 8th 2010, 11:45 AM
yeKciM
Quote:

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)

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

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

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

:D:D:D