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Question
Find the sum of the following geometric progression:
2, 6, 18, ... to 7 terms;
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Solution
Here, a = 2 and r = 3.
\[\therefore S_7 = a\left( \frac{r^7 - 1}{r - 1} \right) \]
\[ = 2 \left( \frac{3^7 - 1}{3 - 1} \right) \]
\[ = 2187 - 1\]
\[ = 2186\]
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