Question

The sum of 19 terms of an A.P whose nth term is 2n+1 is

Answer 1

399 is the answer.
find the sequence by substituting 1,2,3 values in nth term and find C.D and substitute in Sn formula n/2(2a+( n -1) D) by putting n= 19. and u get the answer

Answer 2

Answer:

399

Step-by-step explanation:

1st term=2(1)+1=3

2nd term=2(2)+1=5

d=5-3=2

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

=19/2[2(3)+18(2)]

=19/2(42)

=19×21

=399