Question

The sum of first n terms of an AP is given by Sn = 2n^2 + 3n. find the 16th term of the AP.

Answer 1

sn=2n^2+3n

n=1
s1=2+3=5=a

s=2
s2=8+6=14
14=a+a2
a2=14-5=9           so common difference=4

a16=a+15d
=5+15 x 4
=65
so sixteenth term is 65