geometry formulas for area and perimeter of shapes

Octagon

circle area and perimeter formula
$$\textbf{Area of the octagon}$$
$$A = \frac{1}{4} 8 b^2 \cot\bigg(\frac{\pi}{8}\bigg) $$
$$ = \frac{1}{4} 8 b^2 \frac{\cos\big(\frac{\pi}{8}\big)}{\sin\big(\frac{\pi}{8}\big)} $$
$$\textbf{Perimeter of the octagon}$$
$$P = 8 b $$