Question

If sum of $n$ terms of a sequence is given by $S_n=3n^2-5n+7$ and $t_r$, represents its $r^{th}$ term, then

• A. $t_7=34$
• B. $t_2=7$
• C. $t_{10}=34$
• D. $t_8=40$

Answer 1

The correct option is A $t_7=34$

We have,
$S_n=3n^2-5n+7$

$\therefore S_{n-1}=3(n-1{)}^2-5(n-1)+7=3n^2-11n+15$

Thus $n$th term of the given sequence is given by,

$t_n=S_n-S_{n-1}=6n-8$

Hence $t_7=34,t_2=4,t_{10}=52,t_8=80$