Question

The sum of n number of AP is n^2+3. Find its 20th term

Answer 1

we know ,
Tn = Sn - S(n-1)

Tn =n^2 +3 -(n-1)^2 -3

={ n^2 -n^2 +2n-1 }

= (2n -1)

so,
Tn =(2n -1)

so, 20th term = T20 =2(20) -1 = 39