Hendecagon (11 sides)

Outer radius r_o
Outer radius r_o
Number of sides 11
Side length a_11=r_o*2*sqrt((5-sqrt(5))/2)
Area A=11/4*a*a/tan(pi/11)
sum of sides 11*a_11
Outer angle 360°/11
Radius of inner circle r_i=a/(2*tan(36°))
Diagonal d=sqrt((a_11/2)^2+h^2)
Height h = r_o  + r_i
Sum of angles 1620°



 



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