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# Find $a_9$ if $a_n=(-1)^{n-1}.n^3$

$\begin{array}{1 1}729 \\ 719 \\ 814 \\ 709 \end{array}$

Given: $a_n=(-1)^{n-1}.n^3$
By putting $n=9$ we get the $9^{th}$ term as
$a_9=(-1)^8.9^3=729$