That describes the range, not the input that we are checking.

The intention of this exercise was not to discuss range, as much as core concept, Prime numbers and how we can find them.

If the author had felt there was enough time and space, and that learners had the energy to sit through and absorb some of the finer details, they might have included them in the lesson. But, space is limited and one suspects they believed the learner’s attention span is, too, at least in this instance.

That said,

```
c = a * b
```

which means,

```
b = c / a
```

and

```
a = c / b
```

This means that as `a`

gets bigger, `b`

gets smaller, and vice-versa, which also explains why times tables always mirror one half against the other.

The two equations have opposite slopes, in that one is positive, the other negative, and their graphs intersect. The solution for that intersection is the square root of c.

`a == b so a ** 2 == c AND b ** 2 == c`