Answer
$x^2-2x-99$
Work Step by Step
Using $(a+b)(c+d)=ac+ad+bc+bd$ or the Distributive Property, the given expression, $
(x-11)(x+9)
,$ is equivalent to
\begin{array}{l}\require{cancel}
x(x)+x(9)-11(x)-11(9)
\\\\=
x^2+9x-11x-99
\\\\=
x^2-2x-99
.\end{array}