  This paper presents a general method for obtaining radius of the
corresponding circumference to a cyclical polygon $n$ sides given the lengths
of said sides, using the notion of complex number. As of radius $r$, obtained,
can then be calculated polygon area in question applying known expressions
which requires, after $n=4$, a powerful calculation tool. Are also given like
elements regarding non convex polygons cyclic, although in this respect it
deepens less and is not considered, course, the calculation of areas.
