Question

if the 7 term of an AP is 1/9 and 9 term is 1/7 find its 63 term

Answer 1

a+6d=1/9 i
a+8d=1/7. ii

ii -I.
d=1/63
a=1/63

t63. = 1
and 1

Answer 2

Since nth term in AP is given by  $T_{n}$=a+(n-1)d
  where a is the first term and  d is the common difference 
∴ $T_{7}$=a+6d=1/9____(1)
and $T_{9}$=a+8d=1/7---------(2)
 subtracting (2)-(1)=2d=1/7  -1/9=2/63 
∴d=1/63   and put the value of d  in (1)  we get a=1/9- 6/63 
∴a=1/63 
and $T_{63}$=a+2d=1/63 +2/63=3/63=1/21
∴63rd term is 1/21