Octagon

An octagon is an eight-sided polygon.

Regular octagons

Each internal angle of a regular octagon measures 135 degrees, so the sum of the angles is $1080^{\circ}$ .

Area: $\displaystyle 2s^2(\sqrt{2} + 1)$

Apothem: $\frac{s(\sqrt{2} + 1}{2}$

Inradius: $\frac{s(\sqrt{2} + 1}{2}$

Circumradius: $s\sqrt{1 + \frac{\sqrt{2}}{2}}$

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