Refer to the following table. The left-hand column of the table lists four errors to avoid in working with
function notation. In each case, use the function $f(x)=x^{2}-1$ and give a numerical example showing that the expressions on each side of the equation are not equal.
$$\begin{array}{|c|c|}\hline & \text { Numerical Example } \\& \text { Showing That the Equation } \\\text { Errors to Avoid } & \text { Is Not, in General, Valid } \\\hline f(a+b)=f(a)+f(b) & \\\hline\end{array}$$