Answer
$$\left( {6,\frac{\pi }{4}} \right){\text{ and }}\left( { - 6,\frac{{5\pi }}{4}} \right)$$
Work Step by Step
$$\eqalign{
& {\text{We have the rectangular coordinates }}\left( {x,y} \right) = \left( {3\sqrt 2 ,3\sqrt 2 } \right) \cr
& {\text{The polar coordinates are:}} \cr
& r = \sqrt {{x^2} + {y^2}} \cr
& r = \sqrt {{{\left( {3\sqrt 2 } \right)}^2} + {{\left( {3\sqrt 2 } \right)}^2}} \cr
& r = 6 \cr
& \tan \theta = \frac{{3\sqrt 2 }}{{3\sqrt 2 }} \cr
& \theta = {\tan ^{ - 1}}\left( 1 \right) = \frac{\pi }{4} \cr
& \theta = {\tan ^{ - 1}}\left( 1 \right) + \pi = \frac{{5\pi }}{4} \cr
& {\text{Therefore, the polar coordinates are:}} \cr
& \left( {6,\frac{\pi }{4}} \right){\text{ and }}\left( { - 6,\frac{{5\pi }}{4}} \right) \cr} $$