Inputs With Signs

When the input is negative, put brackets around it. For $f\left(x\right) = x^{2}-1$, the value at -2 is

$$f\left(-2\right) = \left(-2\right)^{2}-1 = 3$$

The whole input replaces $x$, including its sign. So write -2 in brackets before you square it. The two expressions have different values: $\left(-2\right)^{2} = 4$ and $-2^{2} = -4$.

Fractions need the same care. $f\left(\frac{1}{2}\right)$ means that the whole fraction $\frac{1}{2}$ replaces $x$ in every place where $x$ appears in the rule.