Outer radius r_o
Outer radius r_o
Number of sides 10
Side length a_10=r_o*2*sqrt((5-sqrt(5))/2)
Area 5/2*a*a/tan(pi/10)
sum of sides 10*a_10
Outer angle 360/10
Radius of inner circle r_i=a/(2*tan(36))
Diagonal d=2* r_o
Height h = 2 \cdot r_i
Sum of angles 1440


Description at Wikipedia

deesDecagon (10 sides)
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