geometry

$$\\ {x^2 \over a^2} + {y^2 \over b^2} + {z^2 \over c^2} = 1$$

$$ax + by + cz = d$$

$$\small R^2 = (x-x_0)^2 + (y-y_0)^2 + (z - z_0)^2$$

$$a^2 + b^2 = c^2$$