substitute z = tan x
rewrite

this has three solutions:
(1) z = 0
(2+3)


So, in the range
these all are solutions:
for (1) tan x is 0 for x=0, 180, and 360 degrees
for (2) tan x is 1/sqrt(3) for π/6 and 7π/6
for (3) tan x is -1/sqrt(3) for -π/6 and 5π/6