Chapter 8 - Section 8.1 - Solving Quadratic Equations by Completing the Square - Exercise Set - Page 485: 31

$\dfrac{81}{4} ;\\\\ \left( p+\dfrac{9}{2} \right)^2 $

The third term is equal to the square of half of the middle coefficient. Hence, the third term is \begin{array}{l} \left( \dfrac{9}{2} \right)^2 \\\\= \dfrac{81}{4} .\\\\\text{In factored form,}\\ p^2+9p+\dfrac{81}{4} \\\\= \left( p+\dfrac{9}{2} \right)^2 .\end{array}