In cases where you want to compare two equations, you might want one to ... etc.), establish graphs for linear and quadratic inequalities, and even plot graphs for various kinds of functions ...

A linear graph could be used when exchanging euros into pounds, two different types of currency. Linear graphs are commonly used when converting between different units of measurement. For example ...

This is an interesting class of functions, but not nearly interesting enough for calculus purposes. While I do spend lots of time pushing the idea of linear approximations on my students ...