Chapter 4 - Quadratic Functions and Equations - 4-6 Complete the Square - Practice and Problem-Solving Exercises - Page 237: 33

$4$

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 $m=4$ \begin{align*} &=\left(\frac{4}{2}\right)^2\\\\ &=\left(2\right)^2\\\\ &=4 \end{align*}