Question

the sum of first n yerms of an AP os given by Sn =3n²+5n. gind the nth term of the AP.

Answer 1

I think it may help you.

Answer 2

Let a=first term

d=common difference

S1=a

S2=a+a+d.

=2a+d

S2-S1=2a+d-a[By subtracting (1) and (2)]

=a+d

=2nd term.

So S2-S1=2nd term.

Sn=3n²+5n

S1=3*1²+5*1

=3+5

=8.

S1=a

first term is 8.

S2=3*2²+5*2

=12+10

=22

S2-S1=22-8

=14

Hence a+d=14

a=8

so

8+d=14

d=14-8

=6

Any nth term =a+(n-1)d

8+(n-1)*6

=8+6n-6

=6n+2

Your answer:- 6n+2

That's the answer.

Hope I helped you.