Math question: How to compute the area of polygons

[Robert Presender]

Hi,
  The following is copied from Mathematical Tables from Hand Book of  
Chemistry and Physics.

The area of a regular polygon with n sides of length l =
1/4n(l squared) (cot 180/n)

The area of a circumscribed polygon = n(r squared)tan(pi/n) where pi = 
3.14 and
r = the radius of the circumscribed circle = (l/2)cosec(180/n)

Sorry the above is not in strictly math format.. Hope this helps.
Regards ...  Bob