Chapter 5 - Number Theory and the Real Number System - 5.7 Arithmetic and Geometric Sequences - Exercise Set 5.7 - Page 329: 36

$a_{80}=-842$

The $n^{th}$ term of an arithmetic sequence can be found using the formula: $a_n=a_1+(n−1)d$ where d = common difference $a_1$ = first term $a_n$=$n^{th}$ term The given arithmetic sequence has: $a_1=106 \\d=-12$ Use the formula above to find the 80th term: $a_n=a_1+(n−1)(d) \\a_{80}=106+(80-1)(-12) \\a_{80}=106+79(-12) \\a_{80}=106+(-948) \\a_{80}=-842$