Answer
$\dfrac{1}{4}$
Work Step by Step
RECALL:
To complete the square for $x^2 +mb$, just add $\left(\dfrac{m}{2}\right)^2$.
Using the rule above, the term that must be added to the given expression to complete the square is:
With $m=-1$
\begin{align*}
&=\left(\frac{-1}{2}\right)^2\\\\
&=\left(-\frac{1}{2}\right)^2\\\\
&=\frac{1}{4}
\end{align*}