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# Sum of Geometric Progression

The sum of $$n$$ terms of a geometric progression can be obtained by taking the number of terms being added $$n$$, the first term in the sum $$a$$, and the common ratio $$r$$, and using the following formula:

$\frac{a(1-r^n)}{1-r}.$

For example:

$2 + 6 + 18 +54 = \frac{2(1-3^4)}{1-3} = \frac{2(-80)}{-2} = 80$

Note by Arron Kau
2 years, 2 months ago

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