Question

Find the sum of the first 12 terms of the sequence. Show all work for full credit. 1, -4, -9, -14, . . . (2 points)

Answer 1

Answer:

The sum is = -318

Step-by-step explanation:

See the attached image

Answer 2

Answer:

$S_n=$ -348

Step-by-step explanation:

We are given the following arithmetic sequence and we are to find the sum of its first 12 terms:

1, -4, -9, -14, . . .

For that, we will use the formula for the sum of the arithmetic mean:

$S_n=\frac{n}{2} (a_1+a_n)$

We know the value of the first term ($a_n$) but we need to find the value of $a_{12}$. So we will use the following formula:

$a_{12}=a_1+(n-1)d$

$a_{12}=(-4)+(12-1)(5)$

$a_{12}=-59$

Substituting these values in the sum formula to get:

$S_n=\frac{12}{2} (1+(-59))$

$S_n=$ -348