For the AP 82, 75, 68, 61, ... find the first term that is negative and state its value.

$a=82,d=-7$, so $a_n=82-7(n-1)=89-7n$. For $a_n$ < 0 we need $7n>89$, i.e. $n>12.71$, so the first negative term is the 13th: $a_{13}=89-91=-2$. The 12th term is 5, which is still positive, and the 14th term (-9) is negative but not the first such term.