Which function forms an arithmetic sequence when x = 1, 2, 3, ... ?

f (x) = - x/3 + 5

f (x) = - 2^x

f (x) = 2x^2

f (x) = - 3/x + 5

When we have power function or exponential, or then we have a/x, then functions are not going to give arithmetic sequence, because an arithmetic sequence it is really a linear function when x are natural numbers,

so we need to check only A

f (x) = - x/3 + 5

x 1 2 3 4 5

y 14/3 13/3 12/3 11/3 10/3 arithmetic difference is - 1/3

so the answer is A