question_answer

The sum of \[(n-1)\] terms of\[1+\left( 1+3 \right)+\left( 1+3+5 \right)+\left( 1+3+5+7 \right)+\] ..... is

A)  \[\frac{n(n+1)(2n+1)}{6}\]

B)  \[\frac{n(n-1)(2n-1)}{6}\]

C)  \[{{\left( \frac{n{{(n+1)}^{{}}}}{2} \right)}^{2}}\]    

D)  \[\left( \frac{n{{(n+1)}^{{}}}}{2} \right)\]