Question

If the sum of first n terms of an A.P. is given by $Sn=3n^2+5n$, find the nth term of the A.P.

Answer 1

$S_n=3n^2+5n$

$t_1=S_L=3(1{)}^2+5(1)$

$=>3+5=8$

$=>t_1+t_2=S_2=3\times 2^2+5\times 2$

$=>12+10=22$

$\because a=8,d=14$

$n^{th}$ term of $AP$

$=8+(n-1)14$

$=>8+14n-14=14n-6.$