Answer
Center at$\displaystyle \quad (3,\frac{\pi}{2})$
Radius $=3$
Work Step by Step
For $\theta=0,\ r=0$, so the origin is on the circle.
A circle passing through the origin, of radius $a$, centered at $P_{0}(r_{0}, \theta_{0}),$ has the polar equation
$r=2a\cos(\theta-\theta_{0})$
Applying the trigonometric identity
$\quad \cos(\theta-\pi/2)=\sin\theta$,
we write the equation as
$r=2(3)\displaystyle \cos(\theta-\frac{\pi}{2}),\qquad a=3, \theta_{0}=\frac{\pi}{2}$
Center at$\displaystyle \quad (3,\frac{\pi}{2})$
Radius = $3$
