When using the arc() method,
we should note that the starting
angle and ending angle are both
provided in radians and not degrees.
Radian values go from 0 to twice the
value of pi. This means we can
get a full circle with starting angle
at 0 and ending angle at approximately
around 6.3. Try it for yourself:
For simplicity, use multiples of Math.PI
and not try to guess with number
values.