Octagon (8 sides)

Outer radius r_o
Outer radius r_o
Number of sides 8
Side length a_8=r_o*sqrt(2-sqrt(2))
Area A=2*a*a*(1+sqrt(2))
sum of sides 8*a_8
Outer angle 360°/8
Radius of inner circle r_i=a/(2*tan(36°))
Diagonal d=2* r_o
Height h = 2 \cdot r_i
Sum of angles 1080°