Question

if the sum of first n term of an A.P. is given by SN =3n^2+5n , find the nth term of the A.P.​

Answer 1

Answer:

An=Sn-Sn-1

=(3n^2+5n)-{3(n-1)^2+5(n-1)}

=3n^2+5n-{3(n^2+1-2n)+5n-5}

=3n^2+5n-3n^2-3+6n-5n+5

=6n+2

Answer 2

Answer:

Let n=>1

Now,

S1=>3(1)^2+5(1)=>3+5=>8

a1=>S1

so,a1=>8

Now,let n=>2

then ,S2=>3(2)^2+5(2)=>12+10=>22

a2=>S2-S1=>22-8=>14

Now,An=>?

d=>a2-a1=>14-8=>6

an=>a+(n-1)d

=>putting all values

an=>8+(n-1)6

an=>8+6n-6

✔an=>2+6n

hope it helps uh