## Precalculus (6th Edition) Blitzer

$4$; $16$
Completing the square for the $x$ group can be done by adding the square of one-half of the middle term (x-term). Thus, $(\frac{4}{2})^2=4$ will be added to both sides of the equation. Completing the square for the $y$ group can be done by adding the square of one-half of the middle term (y-term). Thus, $(\frac{-8}{2})^2=(-4)^2=16$ will be added to both sides of the equation. Therefore, the missing expressions in the given statements are: $4$ and $16$, respectively.