## College Algebra (6th Edition)

Let $x$ be one of the numbers, then the other is $-18-x$, then their product is $-x^2-18x$. The maximum value is at $x=-\frac{b}{2a}=-\frac{18}{2\cdot(-1)}=9.$ Hence the maximum value is $f(9)=-(9)^2-18(9)=-243.$