In order to plot this in a "traditional" sense you would have to solve for \(\displaystyle \beta\) as a function of \(\displaystyle \theta\). This is not going to be easy for this case, but it is possible. The better way would be to plot this as a "relation" rather than as a function. There are a number of online resources that you can find that will do this for you. Wolfram|Alpha is a good site but I don't remember off the cuff how to tell it to graph this.
Here's your graph; $\theta$ and $\beta$ are in radians. The red "curve" is your graph. You can see that $\beta$ is not a function of $\theta$ and $\theta$ is not a function of $\beta$. The given relation's graph for arbitrary theta and beta is shown outside the red square.