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