Question

The sum of (n-1) terms of 1+(1+3)+(1+3+5)+.............is

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

Let $T_n$ be the n terms of the series $T_n$ = 2 $\sum n-\sum 1$

$\Rightarrow$ $T_n$ = $\frac{2n(n+1)}{2}$ - n = $n^2$

$\therefore$ $S_n$ = ${\sum }_{k=1}^n(k{)}^2$ = $\frac{n(n+1)(2n+1)}{6}$

Hence sum of (n-1) terms $S_{n-1}$ = $\frac{n(n-1)(2n-1)}{6}$