Why are parentheses used in functions in excel?
It is a common practise in maths or programming to use parenetheses to group function's argument(s).
The programmers of Excel (or any other spreadsheet editor) follow those widely accepted rules and also tend to put the arguments of fuctions in parenetheses.
Note that maths is not as strict as the programming, so there are some places when the functions do not have parenetheses.
In maths you can skip the parenetheses if the argument of (for example)
The programming languages do not allow such simplifications and you have to put all the arguments in parenetheses. So in a computer program you would have to write