The generic function notation. It means that f is a function with x as an independent variable or argument. Pronounced f of x.

Generic function notation. If more than one function is to be used, the second is named g(x) and so on. It means that f is a function with x as an independent variable or argument. More arguments may be inserted inside the brackets, separated by comas. Example: f(x,y). Pronounced eff of ex.

The line below is our "function definition", if you will.

f(x) = 2x + x²

So, f(x) is two x plus x squared. Simple enough. Now we've defined that function, what if we want to put a value into it and work out the answer? We write it like this -

f(2) = (2 * 2) + 2²
f(2) = 4 + 4
f(2) = 8

Function notation is very handy in a lot of math work, especially that involving graphs. See Common graph shifts and stretches.