is there a one equation curves that describe multiples curves?

Question

I would like to have one equation that describes the complex curves that are shown in this picture below. this curve is made out of two simple equation curves but is there a way to have one equation that fulfills the desired curve with one equation. I would like to have some hints as well or where to look it up as a topic in mathematics since I have many curves like this that I am trying to describe in one equation.

Answer 1

The curve is given by $$y = \max(0.2x, 2x-4)$$

You can also get the union of the red and blue curve by a polynomial equation: $$(y-0.2x)(y-2x+4)=0$$ This is a special case of an algebraic variety, so you could look this topic up (Warning: depending on the source, it gets very abstract and complicated very fast).