Question

Find the 20th ,25thand nth term of the a.p.given by 21,16,11,6,1,-4,-9,....

Answer 1

Here, 1st term (a)=21
Common difference (d)=16-21=-5
So 20th term=21+19×-5=21-95=-74
as well as 25th term=21+24×-5=21-120=-99

Answer 2

Given :

AP : 21,16,11,6,1,-4,-9,....

To find :

Find the 20th ,25thand nth term of the a.p.

Solution:

AP : 21,16,11,6,1,-4,-9,....

First term = a = 21

Common difference d= 16-21=11-16=-5

Formula of nth term = $a_n=a+(n-1)d$

Substitute n = 20

So$,a_{20}=21+(20-1)(-5)=-74$

Substitute n = 25

$a_{25}=21+(25-1)(5)=-99$

Hence The 20th term is -74 and 25th term is -99