How do I find the summation of 1+3+9+........+n without assuming any summation formula?

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Thanks a lot in advance................

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- Oct 19th 2010, 07:17 PMArkaSummation problem......
How do I find the summation of 1+3+9+........+n without assuming any summation formula?

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Thanks a lot in advance................ - Oct 19th 2010, 07:38 PMEducated
As I can see from the sequence, I see that it is a geometric sequence.

You can use the formula: $\displaystyle S_n=\dfrac{ar^n - a}{r - 1}$

Where:

a = the first term

r = common ratio, which in this case is 3

n = nth term that it goes to - Oct 19th 2010, 10:27 PMArka
- Oct 20th 2010, 12:10 AMEducated
Oh, I thought you meant without the sigma notation $\displaystyle \sum$.

In that case, the only way that I can think of is by just adding them up manually. - Oct 20th 2010, 12:15 AMmr fantastic
- Oct 20th 2010, 12:29 AMArka
Thanks a lot..............Mr. Fantastic....