Half of 2, plus a fifth of 3, plus 1, makes 2.6. If you can do that sum, you can start this course. Everything a neural network does is that sum, repeated with longer lists and bigger numbers, plus a handful of habits for reading and writing it quickly. This chapter teaches those habits from the beginning, with small numbers first and the symbols second.
Section 1 shows why math writes a recipe with letters, how to fill the letters in, and which step comes first. Section 2 gives a rule that turns inputs into one output its proper name and its notation, f(2) = 7. Section 3 puts a table of numbers on a picture and reads one back off. Section 4 describes a straight line with just two numbers, how steep and where it starts. Section 5 adds up a list, shares the total out fairly, and decodes the big Greek S that stands for "add these up." Section 6 is the roadmap: what the fourteen chapters ahead cover, what the 🧪 labs are, and what the appendices are for.
Nothing here is a neural network yet. But the numbers are the ones the first neuron will use, so by the end of the chapter you will already know what 2.6 means and where it comes from.