The input of a system is a sine wave of frequency $1/2$ radians per second. The teacher has written it this way, but I do not understand what the $t$ is supposed to mean.
$$\begin{align}\text{Input} &= \sin\left(\frac12t\right)\\ \omega&=\frac12\text{radians}/\Bbb s\propto\text{frequency}\end{align}$$
There is also that unidentified symbol that looks like alpha($\alpha$) before the word frequency on the second line. What is this symbol and what does it mean??
Thank you!
The alpha-looking symbol means "is proportional to", as stated in the comments. You can get it in mathjax using
\propto, shown here: $\propto$. So if $a\propto b$, then we know that $a=kb$ for some $k\in\Bbb Z$ and $k\ne0$.