How can I plot a straight line which is in normal form? Take a look at this link.
Suppose, I have the following equation of a straight line:
$$x  \cos\theta+ y \sin \theta=p$$
If we rearrange the equation as follows:
$$y = \frac{p - x\cos\theta}{\sin\theta}$$
we are again stuck with infinite values of $x$. So, what is the benefit of introducing $\theta$ and $p$ here?
How can/should I plot this?

A line’s normal is perpendicular to the line: if it makes an angle of $\theta$ with the $x$-axis, then the line itself makes an angle of $\theta+\pi/2$ with the $x$-axis. Now, $\cos(\theta+\pi/2)=\sin\theta$ and $\sin(\theta+\pi/2)=-\cos\theta$, so if your equation of the line has the form $ax+by+c=0$, then a direction vector of the line is $(b,-a)$. This, together with a known point on the line, which you can find by plugging in a convenient value for $x$ or $y$ and solving for the other variable, should be enough information for you to plot the line.
