A) \[{{n}^{2}}-2n+6\]
B) \[\frac{n(n+1)(2n-1)}{6}\]
C) \[{{n}^{2}}+2n+6\]
D) \[\frac{n(n+1)(n+2)}{6}\]
Correct Answer: D
Solution :
Here \[{{T}_{n}}=\frac{n(n+1)}{2}\] Therefore\[{{S}_{n}}=\frac{1}{2}\left\{ \Sigma {{n}^{2}}+\Sigma n \right\}\]\[=\frac{n(n+1)(n+2)}{6}\].
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