3 years ago

What is the sum of the first eight terms of the geometric series 2 + 6 + 18 + 54 + … ?

1 answer:

8 0

Hello,
$u_{1} =2\\
 u_{2} =2*3\\
 u_{3} =2*3^2\\
...
 u_{8} =2*3^7\\

\sum_{i=0}^7\ 2*3^i\\
=2(1+3+3^2+...+3^7)\\
=2* \dfrac{3^8-1}{3-1}\\
=2* \dfrac{6560}{2} \\
=6560
$

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