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Topic: how to derive a formula to find the sum of a sequence?
Replies: 4   Last Post: Nov 3, 2012 3:56 PM

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Posts: 117
Registered: 1/19/06
Re: how to derive a formula to find the sum of a sequence?
Posted: Dec 11, 2010 10:56 AM
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You have added 5 times and each time got "6" as the answer. That tells you that the total sum is 5(6)= 30.
But you added the sum you want TWICE, the second time reversed. That is, the answer "30" is exactly twice the sum you want.

(By the way, what you wrote:
SUM (k+1)

with k+1 rather than k, would be 2+ 3+ 4+ 5+ 6

Reversing those and adding:
2+ 3+ 4+ 5+ 6
6+ 5+ 4+ 3+ 2

You get "8" each of 5 times. What is the sum of that?

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