It's a known equality that

`exp(`**i**z)=cos(z)+**i**sin(z)
where `z` is a complex number, and **i** the square root of -1.

Now let's assume `x` is a real (so it's also a complex number). The cool thing
about this is that the value of `exp(`**i**x) represented in the complex plane
will be on a circle with radius of one unit. Also the line going through this point and the
point representing 0 will close `x` degrees (in radians) with the real
(the horizontal) axis.

If `0<=x<`*pi* then it's also called the *argument of
*`exp(`**i**x).