Question:
If the sum of n terms of an AP is 2n2 + 3n, then write its nth term.
Solution:
Given:
$S_{n}=2 n^{2}+3 n$
$\Rightarrow S_{1}=2(1)^{2}+3(1)$
= 5
$S_{2}=2(2)^{2}+3(2)$
= 14
$\therefore a_{1}+a_{2}=14$
$\Rightarrow 5+a_{2}=14$
$\Rightarrow a_{2}=9$
Common difference, $d=a_{2}-a_{1}$
= 9-5
= 4
nth term $=a+(n-1) d$
$=5+(n-1) 4$
$=4 n+1$