Write an explicit formula for the sequence:
$\displaystyle {\left\lbrace\frac{{1}}{{8}},-\frac{{1}}{{{9}}},\frac{{1}}{{{10}}},-\frac{{1}}{{{11}}},\frac{{1}}{{{12}}},-\frac{{1}}{{{13}}},\ldots\right\rbrace}$
$\displaystyle {a}_{{n}}=$ Preview Question 6