A mirror in code

You will write three small functions for a spherical mirror. They use the New Cartesian sign convention.

The idea. For a mirror, $\dfrac{1}{v} + \dfrac{1}{u} = \dfrac{1}{f}$, and $m = -\dfrac{v}{u}$. A real object has a negative $u$. A concave mirror has a negative $f$. A negative $v$ means a real image, in front of the mirror. All the distances are in centimetre.

Your tasks.

1. In image_distance, return $v$ from $u$ and $f$.
2. In magnification, return $m$ from $u$ and $v$.
3. In image_kind, return the word "real" when $v$ is negative and "virtual" when it is positive.