Prime factorizations - Wednesday work
1. 44 2^2 • 11
2. 125 5^3
3. 85 5 • 17
4. 39 3 • 13
5. 63 3^2 • 7
6. 240 2^4 • 3 • 5
7. 87 3 • 29
8. 45 3^2 • 5

8 0

3 years ago

Find the sum of a finite geometric sequence from n=1 to n=8, using the expression -2(3)^n-1

MissTica

$\bf \qquad \qquad \textit{sum of a finite geometric sequence}
\\\\
S_n=\sum\limits_{i=1}^{n}\ a_1\cdot r^{i-1}\implies S_n=a_1\left( \cfrac{1-r^n}{1-r} \right)\quad 
\begin{cases}
n=n^{th}\ term\\
a_1=\textit{first term's value}\\
r=\textit{common ratio}
\end{cases}
\\\\\\
\sum\limits_{n=1}^{8}~-2(3)^{n-1}~~
\begin{cases}
n=8\\
a_1=-2\\
r=3
\end{cases}\implies S_8=-2\left( \cfrac{1-3^8}{1-3} \right)
\\\\\\
S_8=\underline{-2}\left( \cfrac{1-6561}{\underline{-2}} \right)\implies s_8=1-6561\implies S_8=-6560$