Answer
$ x^2+y^2= 16$
Work Step by Step
The conversion of polar co-ordinates $(r, \theta)$ to rectangular coordinates $(x,y)$ can be expressed as:
$x=r \ \cos(\theta)$, $y=r \ \sin(\theta) $
where, $r=\sqrt{x^2+y^2}$
We have : $r = 4 \ ~~(1)$
Squaring on both sides of equation (1), we have:
$r^2 = 16$
Substitute the $r$ equation:
$ x^2+y^2= 16$
