Problem understanding a parameter in a digital filter

[diredragon]

Homework Statement

Digital causal recursive filter is a part of a digital signal processing system which has sampling frequency $fs = 1200Hz$ and is given by a differece equation:

where $r = 0.9$ and $θ$ is such that it filters out the spectral components at $f = 200Hz$
Find $H(z)$ and graph the poles and zeros of this filter.

Homework Equations

3. The Attempt at a Solution [/B]
I'm having trouble figuring out how to determine the $θ$ in this equation. I did find the $H(z)$ in function of $cos(\theta)$ but still made no progress on determining it. How does the fact that it filters out $200Hz$ help me in this case? Is it something with the location of the zero or a pole on the plane?

 

[Valkarie]

I'm also having trouble graphing the poles and zeroes. I know that $H(z) = \frac{b_0 + b_1z^{-1} + b_2z^{-2}}{a_0 + a_1z^{-1} + a_2z^{-2}}$ but I don't understand how to plot it's poles and zeroes after I determined them.