I don't think it is possible to use symbols like square root, squared, integral, derivative, etc in the annotations,
To describe the worksheet you can use Caption option,Refer to the article Captions
or you can use this
Bummer. Tableau has some weird limitations.
Thanks for the reply Alvinio.
You could sheet-swap in a pictorial representation of your equation using the sheet-swap technique.
I question why you need to display this though, its kind of like watching thunderbirds on TV and focussing on the wires. Your readers should be looking at what the lines mean, not how they got there.
Thank you for that idea Peter.
To your second point, I need to define the line on my graph somehow. Currently I don't have any description so viewers have no idea what that line is. I made my line up, which means it is not some ratio with an existing name like "P/E" or "PEG" that is easy to type into an annotation. I need to tell viewers what that line is. Perhaps a better question is, what is the Tableau way of defining a line in a line graph? I figured using symbols would be more concise than spelling out the equation in words, which is why I asked in the first place.