Question

PLEASE HELP ASAP!!! CORRECT ANSWER ONLY PLEASE!!!

What is the sum of the first 7 terms of the series − 3 + 6 − 12 + 24 −... ?

Answer 1

Answer: -129

Explanation:

Given the sequence {-3, 6, -12, 24, ... }, we can see that the first term (a) is -3 and the ratio (r) is
`(6)/(-3) = -2`.

Input those values into the Sum formula:

`S_n=(a(1-r^n))/(1-r)\\\\S_7=(-3(1-(-2)^7))/(1-(-2))\\\\.\quad=(-3(1-(-128)))/(1+2)\\\\.\quad=(-3(1+128))/(3)\\\\.\quad=(-3(129))/(3)\\\\.\quad=-129`