Question

in an AP sn=n^2 find its a15​

Answer 1

Answer:

Usually,

Tn = nth term

T1 = 1st term

T2 = 2nd term

and so on...

Sn = Sum of first n terms of the sequence

Sn = 1st term + 2nd term + 3rd term + ... + nth term

Sn = T1 + T2 + T3 + ....Tn

You are given here that "Sn is the SUM of first n terms..." So you have

Sn = T1 + T2 + T3 + ....Tn = n(n+1)

So S1 = T1

S2 = T1 + T2

S3 = T1 + T2 + T3

and so on

S1 = T1 = 1*(1+1) = 2

S2 = T1 + T2 = 2 + T2 = 2*(2+1) = 6

So T2 = 4

S3 = T1 + T2 + T3 = 2 + 4 + T3 = 3*(3+1) = 12

So T3 = 6

(This is what we wanted)

The third term is 6.