If the nth partial sum of a series is s_n = (n-2)/(n+6), what is a_n?

a_n = s_n - s_(n-1)
.......= (n-2)/(n+6) - (n-3)/(n+5)
.......= [(n-2)(n+5) - (n-3)(n+6)] / ((n+5)(n+6))
.......= 8/((n+5)(n+6)).

I hope this helps!