Difference between revisions of "TADM2E 2.34"

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(Created page with "This task refers to this song The_Twelve_Days_of_Christmas_(song) So we have to calculate the sum like this 1 day - 1 gift 2 day - 1 gift + 2 gifts 3 day - 1 + 2 + 3 n day -...")
 
 
Line 1: Line 1:
 
This task refers to this song The_Twelve_Days_of_Christmas_(song)
 
This task refers to this song The_Twelve_Days_of_Christmas_(song)
 +
 
So we have to calculate the sum like this
 
So we have to calculate the sum like this
  
 
1 day - 1 gift
 
1 day - 1 gift
 +
 
2 day - 1 gift + 2 gifts
 
2 day - 1 gift + 2 gifts
 +
 
3 day - 1 + 2 + 3
 
3 day - 1 + 2 + 3
 +
 
n day - 1 + 2 + 3 + ... + n
 
n day - 1 + 2 + 3 + ... + n
 +
  
 
Formula is  
 
Formula is  

Latest revision as of 07:08, 27 May 2020

This task refers to this song The_Twelve_Days_of_Christmas_(song)

So we have to calculate the sum like this

1 day - 1 gift

2 day - 1 gift + 2 gifts

3 day - 1 + 2 + 3

n day - 1 + 2 + 3 + ... + n


Formula is

$ \begin{align} &\sum_{i=1}^n \sum_{j=1}^n j\ = \sum_{i=1}^n \frac{n(n+1)}{2} =\\ &= \frac{1}{2}\sum_{i=1}^n n^2 + \frac{1}{2}\sum_{i=1}^n n=\\ &= \frac{n(n+1)(2n+1) + 3n(n+1)}{12} = \frac{(n+1)(n^2+2n)}{6}\ \end{align} $