Question

If 3rd and 9th term of AP are 4 and 8 respectively find which term is zero

Answer 1

T3 = a+2d = 4
T9 = a+8d = 8
subtract these equations
a gets eliminated
then,
-6d = -4
d = 2/3
if d = 2/3
then
a = 8/3
they asked which term is zero
Tn = 0
a +(n-1)d = 0
a = 8/3 ; d = 2/3
n = -3
so 3 terms back of zero the Tn value is 0

Answer 2

solve this answer by this question