Question

The sum of nth terms of an Ap is given by sn = 2n^^ +3n find the 16th term of Ap

Answer 1

Sn = 2n^^2 +3n
S1= 2(1)^2+3(1)
= 5
S1= a1
therefore the first term is 5
S2= 2(2)^2+3(2)
=14
S2 = a1+a2
S2-a1= a2
a2= 9
d=a2-a1= 4

a16= a+15d
= 5 +15(4)
= 5+60
=65
the sixteenth term is 65