Given the edge length of the regular 20 side polygon is l=6 cm. Find the 20 sided polygon volume and surface area. Solution: Area, A = 5√3 l ^2 = 8.66 l2. = 8.66 x 6^2 = 8.66 x 36 = 311.7 cm^2. Volume, V = [5(3 +√5)/12] l ^3 = 2.181 l ^3. = [5(3 +√5)/12] 63 = 2.181 x 216. = 471 cm^3.
http://mathtutoring.jimdo.com/geometry/20-sided-polygon/ That's the site I got this from. But surely you've alerady been here. I personally have no clue how to do this. Hope this helps!
