sum(r=1)^n r(n-r) is equal to :...

`sum_(r=1)^n` r(n-r) is equal to :

A

`1/6 n(n-1)(2n+1)`

B

`((n(n+1))/2)^2`

C

`(n^2 (n+1))/6`

D

`(n(n^2 -1))/6`

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The correct Answer is:

D

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