Answer
$r=3$
Work Step by Step
Formulas relating rectangulsr $(x,y)$ and polar $(r,\theta)$ coordinates:
$ x=r\cos\theta$ and $ y=r\sin\theta$
$r^{2}=x^{2}+y^{2}$ and $\displaystyle \tan\theta=\frac{y}{x}$.
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$x^{2}+y^{2}=9$.
Substitute $x^{2}+y^{2}$ with $r^{2}$,
$r^{2}=9$
$r=\pm 3$
(the directed distance from the pole is 3 or -3)
Taking r to be positive,
$r=3$
