picture presentation :

http://skrypty24.com.pl/11.JPG

ctg alfa = h / 1/2 * a

alfa will be descrease with angle, dependence ctg alfa will be incease

example for figure where alfa angle is 30 degrees

ctg alfa = sqrt(3) = h / 1/2 a

h = sqrt(3) / 1/2 * a

with increase the number of sides of same side figure, side 'a' going to zero, ctg alfa going to higher and higher value, and reach 'H', like in the h = ctg alfa * 1/2a, h will be increase, so xa / 2h ( dependence the diameter to ray ) will be going to infinity value of sides to H * ctg 0 degrees, no value for it, so to 'H'