Chapter 12 Sequences and Series - 12.2 Analyze Arithmetic Sequences and Series - 12.2 Exercises - Problem Solving - Page 808: 65b

$576$

We know that the general formula of an arithmetic sequence is given by $a_n= a_1+(n-1) d$ Here, $a_n=4+8(n-1) $ $a_n=8n-4$ Thus, we have $a_n=8n-4$ Now, $a_{12}= (8)(12) -4=92$ and $S_{12}=\dfrac{12 \times (4+92)}{2}=576$