# Math Help - Indicies

1. ## Indicies

How could you factorise
$(-1)^{k-1} + (-1)^{k}$

2. Originally Posted by Ifailatmaths
How could you factorise
$(-1)^{k-1} + (-1)^{k}$
The common factor is $(-1)^{k-1}$. Note: $(-1)^k = (-1)^{k-1} (-1)$.