Chapter 8 - Section 8.1 - Solving Quadratic Equations by Completing the Square - Exercise Set - Page 484: 104

$\pm6$

Twice the square root of the last term (which is $ 9 $) of the given trinomial is $ 6 .$ Therefore, the two possible missing terms that will make the given trinomial a perfect square is \begin{array}{l}\require{cancel} \pm6 .\end{array}