Platon formula/Check for octahedron, dodecahedron, icosahedron/Exercise

Check the formula

${}2{\left(1-{\frac {1}{n}}\right)}=\sum _{i=1}^{m}{\left(1-{\frac {1}{n_{i}}}\right)}\,$

of

fact for the octahedron, the dodecahedron, and the icosahedron.

Create a solution