Question

if the common difference b/w each no. is zero then the list of numbers are in AP

Answer 1

if the numbers are in ap and the common difference is zero then , all the numbers are same and hence a can take any value. for eg if a=1 then ap will be 1,1,1,1.. as common difference is zero.

Answer 2

There can be any no. in list of A.P.-
0,0,0,0,0,0,......
1,1,1,1,1,1,1.......
2,2,2,2,2,2,2,.....
3,3,3,3,3,3,3.......
4,4,4,4,4,4,4.......