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

Apothem: $\frac{s(1+ \sqrt2 )}{2}$

Inradius: $\frac{s(1+ \sqrt2 )}{2}$

Circumradius: $\frac{s\sqrt{4+2\sqrt{2}}}{2}$

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