I am currently learning from a book called Beginning Maths and Physics for Game Programmers. I had trouble with this book quite early on due to the fact that I had completely forgotten most of the maths I had learnt at school so I went through some Algebra and Linear Algebra books to help me and I feel I am doing better with this book, this time around.

Now, I am confused about a question in the book. It says, "Find the equation of a line connecting the following pairs of points:"

It continues to list a few points for a 2D coordinate system, but the last two is a 3D coordinate system and the two points for one of the questions are:

(2, 0, -1) and (3, 4, 5)

Now, the book doesn't tell you at all how to find out how to get the equation of three points, only two. I have tried applying different ways of doing it, but it never turns out right. I would have thought, when you come to exercises or tasks, you should be at least taught how to do it and not thrown into the dark because you learnt how to do the bare minimum.