Why do we put the f on the left of x? [duplicate]
Solution 1:
This is consistent with English syntax and with the concept of "function" being a special kind of relation on sets.
Look at the relationship "Husband of": In English this is typically expressed, for example, as Husband of Hillary Clinton is Bill Clinton.
In mathematical notation this gets naturally translated maintaining the syntax order: H(Hillary) = Bill
Successor of Obama is Trump (in US presidency)
$S(n) = n+1$ (Successor function in natural numbers)
Solution 2:
To my recollection this notation goes back to Leonard Euler.
Solution 3:
There are times when $f(x)$ is written $xf$. It's merely a case of trying to use the accepted convention except when it is inconvenient to do so; in which case you state that you are doing it differently and then proceed to do so.