Answer:
The smallest possible domain to completely graph two periods is either [0, 2π] or [-π, π].
Step-by-step explanation:
The period of cosine function [0, 2π].
The given function is

This function can be written as
.... (1)
The general form of cosine function is
.... (2)
where, A is amplitude,
, C is phase and D is midline.
From (1) and (2), we get


The period of given function is [0,π]. So, the smallest possible domain to completely graph two periods is either [0, 2π] or [-π, π].