## Precalculus (6th Edition) Blitzer

$320$ Degree days
The sum of an arithmetic sequence is given by: $S_n=\dfrac{n}{2}[a_1+a_n]$ and the nth term for an arithmetic sequence is given by $a_n=a_1+(n-1) d$ We are given that $a_n= 314, 628$ Now, $a_{10}=23+(10-1) \times 2=41$ The sum of an arithmetic sequence is given by: $S_n=\dfrac{n}{2}[a_1+a_n]$ $S_{10}=\dfrac{10}{2}[23+41]=320$ Degree- days