December 26th, 2017, 03:14 PM  #11 
Senior Member Joined: May 2016 From: USA Posts: 1,084 Thanks: 446 
I am late to this thread but $\displaystyle \sum_{j=k}^n \text { expression in j and n }$ means to loop through, incrementing j by 1 each time, starting with j = k and ending with j = n, to calculate the value of the expression in each iteration of the loop, and to add that value to a cumulative sum. $\displaystyle \sum_{j=2}^5 nj^2$ is computed as follows Initialize sum = 0 First iteration j = 2 so $nj^2 = 5 * 2^2 = 20 \text { and } 0 + 20 = 20.$ Second iteration j = 3 so $nj^2 = 5 * 3^2 = 45 \text { and } 45 + 20 = 65.$ Third iteration j = 4 so $nj^2 = 5 * 4^2 = 80 \text { and } 80 + 65 = 145. $ Last iteration j = 5 so $nj^2 = 5 * 5^2 = 125 \text { and } 125 + 145 = 270.$ Summation notation is a highly abbreviated way to explain a procedure. Nothing fancy about it. 
December 28th, 2017, 03:32 PM  #12  
Newbie Joined: Feb 2012 From: Central Florida Posts: 10 Thanks: 0  Quote:
Last edited by skipjack; December 28th, 2017 at 04:02 PM.  
December 28th, 2017, 04:07 PM  #13 
Global Moderator Joined: Dec 2006 Posts: 19,302 Thanks: 1688 
Some calculators may be more flexible than others as to how a summation is entered.


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