Answer
Polar equation is: $r^2=4$
or, $r=2$ and $r=-2$
Work Step by Step
Conversion of polar coordinates and Cartesian coordinates are as follows:
a) $r^2=x^2+y^2 \implies r=\sqrt {x^2+y^2}$
b) $\tan \theta =\dfrac{y}{x} \implies \theta =\tan^{-1} (\dfrac{y}{x})$
c) $x=r \cos \theta$
d) $y=r \sin \theta$
Since, we have $r^2=x^2+y^2 \implies r=\sqrt {x^2+y^2}$
Thus, we have an equivalent polar equation: $r^2=4$
Or, $r=2$ and $r=-2$
