Confusing Notation Between Functions and Numbers

Consider the simple function $f(x) = x.$

As you see above, remember that functions are maps that take numbers as input and give numbers as output. While we may add them, divide them, and perform other arithmetic operations on them like we do with numbers, they are not numbers themselves.

Just as some practice. Consider the function $g(x) = 3$

Check out Warning: Derivative of 3^2 for an example of this.