Chapter 4 Quadratic Functions and Factoring - 4.3 Solve x(squared) + bx + c = 0 - 4.3 Exercises - Skill Practice - Page 256: 16

$$(b-9)(b+9)$$

Since the coefficient of the squared term is one, we know that the expression must factor to: $$ (b\pm a)(b\pm k)$$ Here, we see that a and k must multiply to get $-81$ and add to get $0$. Thus, we find that the solution is: $$(b-9)(b+9)$$