These are equations i either saw or made up, which may or may not describe something or make sense.
Not being much of a mathematician , I use these as excercizes to see whether they make sense and if they describe anything — -similar to crossword puzzles.
y= (dx/dt)² + c
y’ = dy/dx = 2x
etc =2xt 2x …
Anwar Sheik’s (economist) HUBRUS model is a good one.