Find all solutions to the given equation.

tan(x/3)=0

we know that tan 0 = 0

so x/3 = 0
x = 0

but we also know that more solutions can be obtained by adding the period of tan(x/3) to any answer.
tan x/3 = tan ( (1/3)x )
180/(1/3) = 540
so solutions are : 0°, ± 540°, ± 1080°, ...
or simply 540k°, where k is an integer
in radians it would be 3k?, where k is an integer.

check:
http://www.wolframalpha.com/input/?i=plot+y+%3D+tan(x%2F3)

notice the solutions of -3?, 0, and 3?