Question

An=2n+1find the sum of he first three terms

Answer 1

Answer: 15

An=2n+1

n=1, 2(1)+1=3

n=2, 2(2)+1= 5

n=3, 2(3)+1= 7

First three terms

3,5,7 a=3 , d= 2

Sn=n/2 [2a+(n-1)d]

S3= 15

so, sum of first three terms = 15