Question

the sum of first n terms ap sn,is 3n2+6n.find the nth term of ap.

Answer 1

Sn=3n2+6n

S1=3 (1)2+6 (1)

S1=a1=15

S2=3 (2)2+6 (2)

S2=48

a2=S2-s1

=48-15
=33
d=a2-a1
= 33-15
=18
an=a+(n-1)d