Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » Math Topics » discretemath

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

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
HallsofIvy

Posts: 116
Registered: 1/19/06
Re: how to derive a formula to find the sum of a sequence?
Posted: Dec 11, 2010 10:56 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

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:
5
SUM (k+1)
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?



Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.