Chapter 9 - Section 9.2 - Arithmetic Sequences - 9.2 Assess Your Understanding - Page 654: 51

$6080$

There are 80 terms, and they form an arithmetic sequence with $a_{1}=2(1)-5=-3$ $a_{80}=2(80)-5=155$ $d=a_{n+1}-a_{n}=2(n+1)-5-(2n-5)=2n+2-5-2n+5=2$ Sum of the First $n$ Terms of an arithmetic sequence: $S_{n}=\displaystyle \frac{n}{2}\left(a_{1}+a_{n}\right)$ $S_{80}=\displaystyle \frac{80}{2}(-3+155)=40(152)=6080$