圆

[button type="round" color="success"]S：面积[/button] [button type="round" color="info"]R：半径[/button] [button type="round" color="dark"]π：圆周率[/button] [button type="round" color="primary"]θ：角度[/button]

面积

$\color{green}S=\pi R^2 $

周长

$\color{green}周长=\pi \cdot 直径$
$\color{green}周长=2 \cdot \sqrt{(\pi \cdot S)}$

直径

$\color{green}直径=2 \cdot\sqrt{(\frac{S}{\pi})}$

弧形面积

$\color{green}S=\frac{\theta}{360}\pi R^2$

$\color{green}S=\frac{1}{2}R^2 \theta$