=== Radians ===
In mathematics, it is common to use radians to describe angles.
This is because radians give the arc length of a given angle on a unit circle.
If the angle is `a`, then the arc length on a circle of radius `r` is `(a * r)`.
The radians of a full circle with radius `r` is `(2 * pi * r)`.
Many mathematicians use `(2 * pi)` to describe a full circle.
However, it is more convenient to use `tau` or `τ` instead.
For example, `0.25tau` or `(tau / 4)` is a quarter of a circle.
You can also think about it as the circle circumference of a quarter radius.
Poi understand expressions like `0.25tau` or `0.25τ`.
This way, one can work with radians as the range `0τ` to `1τ` for a unit circle.