Explanation:
the period of a function or graph is simply the x-distance from one "top of the hill" to the next "top of the hill", or from one "bottom of the valley" to the next "bottom of the valley".
if the function has that same distance across the whole x-axis (or whatever part is valid), we are calling this a periodic function.
in our case here :
from -9pi to 3pi = 12pi
from 3pi to 15pi = 12pi
from 15pi to 27pi = 12pi
...
so, yes, it is periodic, and the period is 12pi.