Question

if 7th and 13 th term of an A.P be 34 and 64 reapectively ,then its 18 term is​

Answer 1

Let 1st term be "a" and common difference be "d" then 7 term and 13 term can be written as a+6d=34......equ.(1) a+12d=64......equ.(2) Solve both equ. We get a=4 & d=5 then So, 18 term be a+17d= 4+17 5 = 89

Answer 2

T7=34

a+6d=34

T13=64

a+12d=64

Subtractimg the eqs

6d=30

d=5

a+6d=34

a=34-30

a=4

18th term is

T18=a+17d

=4+17(5)

=4+85

=89