[Randall Munroe] certainly understands the power of graphical representation of data. The humorous plots in his xkcd webcomic are one of the favorite parts for many readers. Their distinctive, ...

Inequalities that use < or > symbols are plotted with a dashed line to show that the line is not included in the region. Inequalities that use ≤ or ≥ symbols are plotted with a solid line to show that ...