Question

please help im trying to finish a final and dont know this
What is the sum of the geometric sequence -3, 18, -108, ... if there are 7 terms?

-719,835
-119,973
119,973
719,835

Answer 1

It seems that r=-6, so
\[
a_1=-3\\
a_n= -6 a_{n-1}
\]

Answer 2

Here are the first 7 terms
{-3, 18, -108, 648, -3888, 23328, -139968}

Answer 3

Their total is
-119973