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Flag Magical Mathematics[Interesting Approach]> If the sum n.1+(n-1)+(n-2).3+.........+2....
question mark

If the sum n.1+(n-1)+(n-2).3+.........+2.(n-1)+1.n is equal to
A 1/6n(n+1)1
B 1/6n²(n+1)
C 1/6n(n+1)(n+2)
1/6n(n+1)(2n+1)

Sudhanva G V , 6 Years ago
Grade 11
anser 1 Answers
Arun

Last Activity: 6 Years ago

Dear student
 
the r th term will be r(n-r+1)
 
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
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