Answer
Polar equation: $r^2=4$;
or, $r=2$ and $r=-2$
Work Step by Step
The conversion of polar coordinates and Cartesian coordinates are described as follows:
1. $r^2=x^2+y^2$ and $r=\sqrt {x^2+y^2}$
2. $\tan \theta =\dfrac{y}{x} \implies \theta =\tan^{-1} (\dfrac{y}{x})$
3. $x=r \cos \theta$ and 4. $y=r \sin \theta$
Given: $r^2=x^2+y^2$
or, $r=\sqrt {x^2+y^2}$
Now, we get the equivalent Polar equation: $r^2=4$;
or, $r=2$ and $r=-2$
