Chapter 11 - Section 11.2 - Solving Quadratic Equations by Completing the Square - Exercise Set - Page 779: 73

$(z+2)(z-2)(z+3)(z-3)$

Step 1: Let $u=z^{2}$ $=u^{2}-13u+36$ Step 2: Factor $u^{2}-13u+36$ $=(u-4)(u-9)$ Step 3: Substitute back $u=z^2$ $=(z^{2}-4)(z^{2}-9)$ Step 4: Factor $z^{2}-4$ $=(z+2)(z-2)(z^{2}-9)$ Step 5: Factor $z^{2}-9$ $=(z+2)(z-2)(z+3)(z-3)$