Question

What is the sum of the first 7 terms of the series −3+6−12+24−... ? Enter your answer in the box.

Answer 1

-129

This is the correct answer! I just took the test! Good luck!!!

Answer 2

`S_(7)` = - 129

Explanation:

The terms in the series are the terms of a geometric progression with sum to n terms

`S_(n)` =
`(a(1-r^n))/(1-r)` : r ≠ 1

where r is the common ratio and a the first term

here r =
`(24)/(-12)` =
`(-12)/(6)` = - 2 and a = - 3

`S_(7)` =
`(-3(1-(-2)^7)/(1-(-2))`

=
`(-3(1-(-2)^7)/(1-(-2))`

=
`(-3(1-(-128)))/(3)` = - 129