## Algebra and Trigonometry 10th Edition

$a_5=60$ $a_6=73$ $a_7=86$ $S_7=329$
$a_1=8=8+13(0)=8+13(1-1)$ $a_2=21=8+13(1)=8+13(2-1)$ $a_3=34=8+13(2)=8+13(3-1)$ $a_4=47=8+13(3)=8+13(4-1)$ That is, $a_n=8+13(n-1)~~$ (Arithmetic Sequence) $a_5=8+13(5-1)=8+13(4)=60$ $a_6=8+13(6-1)=8+13(5)=73$ $a_7=8+13(7-1)=8+13(6)=86$ $S_7=\frac{n}{2}(a_1+a_n)=\frac{7}{2}(8+86)=329$