find polar coordinates of the points whose cartesian coordinates are given.

heres the point: (3sqrt(3), 3)

well i know that r^2 = (sqrt(a^2 + b^2))

so the answer here is : 6

and if we use tan(theta) = o/a = 3/(3sqrt(3)

so the answer here is: 1/sqrt(3)

so theta is pi/6

so how do i know its pi/6?

how do i convert to get this answer with pi? radians?

help please.