There was a course which I have forgotten. It was not my course. It was done by a graduate friend of mine. I helped him do his homework years ago. It was a course in his master's program.
I had forgotten what I did or learn. But I remember it was very interesting. Basically, you can express various graphs in an equation. I believe it is called "Polynomial interpolation".
If I have not mistaken, we take a set of points, and find a single equation for the line passing through those points. It was fun formulating those equations.