When students work with functions, they often make some common mistakes. Here are a few to watch out for:

1. Understanding Function Notation: It’s important to know what $f(x)$ means. It shows the result of the function $f$ when you use $x$ as the input.

   For example, if $f(x) = 2x + 3$, then to find $f(2)$, you would do this: $f(2) = 2(2) + 3 = 7$.

2. Substituting Values Incorrectly: Pay careful attention to your math operations.

   For the function $f(x) = x^2 - 4$, if you want to find $f(3)$, you should calculate it like this: $f(3) = 3^2 - 4 = 5$, not $3^2 + 4$.

3. Ignoring the Domain: Don’t forget to check the domain of the function.

   For example, in the function $g(x) = \frac{1}{x-1}$, you need to remember that $x$ cannot be 1 because it makes the function not work.

By avoiding these mistakes, working with functions will be much easier to understand!