Find the sum of the first 12 terms of the sequence. If the answer is negative, do not enter any spaces in between the number and the negative sign. 1, -4, -9, -14, . . .

Question

asked Oct 9, 2020 13.1k views

2 Answers

Alona · Answer 1 · 2020-10-12T10:32:43+0000

======================================

Step-by-step explanation:

The formula to use is

S = (n/2)*(2*a1+d*(n-1))

where

S = sum of the first n terms = unknown

n = number of terms = 12

d = common difference = -5

a1 = first term = 1

---------------------------------

So we get the following

S = (n/2)*(2*a1+d(n-1))

S = (12/2)*(2*1 + (-5)*(12-1))

S = 6*(2 - 5(11))

S = 6*(2 - 55)

S = 6*(-53)

S = -318

Greenie · Answer 2 · 2020-10-15T12:18:35+0000

Answer:

-59

Step-by-step explanation:

1 - 5 = -4

-4 - 5 = -9

-9 - 5 = -14

-14 - 5 = -19

-19 - 5 = -24

-24 - 5 = -29

-29 - 5 = -34

-34 - 5 = -39

-39 - 5 = -44

-44 - 5 = -49

-49 - 5 = -54

-54 - 5 = -59