Question

the 3rd and 9th terms of an ap are 4 and -8 respectively, which terms of this AP is zero

Answer 1

hope you will understand

Answer 2

a3=4
a9=-8

Now,
Applying elimination
a+2d=4
a+8d=-8
- - +
_________
-6d=12
d=-2

Putting d= -2 in a+2d=4
a=4-2(-2)
a=8