Question

Tn=2n+1.find the sum of first three terms

Answer 1

let n=1

T1=3

let n=2

T2=5

let n=3

T3=7

First three terms of AP=3,5,7

sum=n/2[2a+(n-1)d]         [where n=no. of terms a=first term of A.P  d=difference between two terms]

        =3/2[6 + 2(2)]

        =15 ans