Question

If the first term of an arithmetic sequence is $-14$ and the common difference is $2$, find the sum of the first $8$ terms.

• A. $-56$
• B. $-46$
• C. $-36$
• D. $-26$

Answer 1

The correct option is A $-56$

First term: $a=-14$
$S_n=?$
$d=2$
$n=8$

$S_n=\frac{n}{2}[2a+(n-1\left)d\right]$
$S_8=\frac{8}{2}[2\times (-14)+(8-1\left)2\right]$

$S_8=4[-28+14]$

$S_8=-56$