Question

Find the 20th term of the AP 9,13,17,21​

Answer 1

generally nth term of an A.p is a+(n-1)d

from the given information we have a=9, d=4 and n=20

now ; 20th term = 9+(20-1) 4

= 9+19×4

= 85

hence 20th term of given A.p is '85'

thankyou :)

Answer 2

Answer:

let a be the first term and d be the common difference of the given AP then a =9 and d = 13-9=4

we need the 20th term of given AP so n=20

we know that,

an =a+(n-1)d

a20= 9+(19)×4

=9+76

=85

hence the 20th term of the given AP is 85