Summation problem (first N positive integers)

  • #1

Homework Statement



LNE5ZhT.png



Homework Equations



so i kno the formula for the for the sum of the first N positive integers

MZOJig4.png


when i = 1


The Attempt at a Solution



i kno the answer = n^2(n+1)/2

but could someone explain step by step how you reduce it to get the final answer? as if i'm in kindergarten? i'm slow, thanks.

my work:

following the formula: n(n+1)/2 * n(n+1)/2 * n(n+1)/2 ?

i don't understand how to reduce the terms to get the final answer provided
 
Last edited:

Answers and Replies

  • #2
Ray Vickson
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Homework Helper
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Homework Statement



LNE5ZhT.png



Homework Equations



so i kno the formula for the for the sum of the first N positive integers

MZOJig4.png


when i = 1


The Attempt at a Solution



i kno the answer = n^2(n+1)/2

but could someone explain step by step how you reduce it to get the final answer? as if i'm in kindergarten? i'm slow, thanks.

PF rules require you to show us your work.
 
  • #3
oh okay sure
 
  • #4
rcgldr
Homework Helper
8,745
549
Are you sure the upper bound on the second summation is "i" and not "n"? Note that this is a summation of the value "1", not the variable "i".
 
  • #5
Dick
Science Advisor
Homework Helper
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619
Are you sure the upper bound on the second summation is "i" and not "n"? Note that this is a summation of the value "1", not the variable "i".

If the upper bound on the second summation were "n" then the sum would be n^3. You are only going to get the correct answer if the upper bound is "i". Start with the innermost sum and work your way out. It's not hard.
 

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