Question

the sum of first n terms of an Ap is given by the formula sn=3n^2+n it's 3rd term is​

Answer 1

Answer:

Sn=3n2+2n

Taking n=1, we get 

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

⇒S1=3+2

⇒S1=5

⇒a1=5

Taking n=2, we get 

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

⇒S2=12+4

⇒S2=16

∴a2=S2−S1=16−5=11

Taking n=3, we get 

S3=3(3)2+2(3)

⇒S3=27+6

⇒S3=33

∴a3=S3−S2=33−1