I suspect in the study guide there also a statement about absolute value.

If p & q are two points on a number line the the distance between them is $|p-q|$

Now some may wonder 'how do we know which to subtract from which?'

Well it does not matter, the distance from p to q is the same as the distance from q to p!

So we have $|p-q|=|q-p|$ Moreover, because $|x|=|x-0|$ that means the absolute value of $x$ is its distance from zero.

What Platos says is both true and helpful.

But

Note that

**difference** and

**distance** are not the same thing.

I said that these things make a difference in more advanced maths.

Distance, as Plato defines it, is called a metric.

Metrics are specially choses so that it doesn't matter "which you subtract from which".

But there is a whole section of mathematics called finite differences, in which it matters very much indeed.

In your opening post you asked

What is the difference between -2 and 1.

So you have introduced what are called signed numbers and the result of this difference must be a signed number.

Finite differences are such a case in point.