## Algebra: A Combined Approach (4th Edition)

$-i$
$i^{11}=i^{8}\times i^{3}=(i^{2})^{4}\times i^{3}$ As $i^{3}=-i$ and $i^{2}=-1$, $(i^{2})^{4}\times i^{3}=(-1)^{4}\times(-i)=1\times-i=-i$. Therefore, $i^{11}=-i$.