Question

what is the sum of the geometric sequence -4, 24, -144 if there are 7 terms?

Answer 1

@ganeshie8
@mathmale
@misty1212

Answer 2

Geometric sequence can be written in \(a_n=a_1r^{n-1}\).
So:
\[
\begin{align*}
a_1&=-4\\
a_2&=24\\
a_3&=-144
\end{align*}
\]
Find r first.

Answer 3

a=-4
\[r=\frac{ 24 }{ -4 }=-6\]
n=7
\[S _{n}=a \frac{ r^n-1 }{ r-1 }\]
calculate \[S _{7}\]