Certain terminals support enhanced text, which means that they accept a markup language specific to gnuplot that can be used to include characters from various fonts, set subscripts, superscripts, overprint characters, and generally manipulate text with sufficient flexibility to create simple equations to serve as annotations for your graphs. This recipe shows how to make such an equation, but you will see that the markup is cumbersome, and attaining the desired result requires some amount of trial and error. Frankly, a better way to create all but the simplest mathematical text is to use the LaTeX techniques covered in a later chapter, which also leads to a much more attractive output.
However, the enhanced text mode can be useful for quickly placing some mathematical text on your plot, in situations where you are not too picky about the typographical quality of the result.
