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Find the Sum of n numbers of this series/sequence. Please answer this quickly... 1*n + 2*(n-1) + 3*(n-2) + … + n*1. Find Sn

Find the Sum of n numbers of this series/sequence. Please answer this quickly...
1*n + 2*(n-1) + 3*(n-2) + … + n*1. Find Sn
 

Grade:11

2 Answers

Vikas TU
14149 Points
one year ago
Dear student 
it is summation of r(n-r+1) where r varies from 1 to n;
SUM => ( (n+1)r - r^2 ) = (n+1)(n)(n+1)/2 - (n)(n+1)(2n+1)/6
 
Hope this helps 
Good Luck 
Arun
25763 Points
one year ago
Dear student
 
Tn = ∑(r belongs from 1 to n) (r) ( n – r+ 1))
 
Tn = ∑ ( nr – r^2 + r)
 
now put limit
 
Hope it helps

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