Answer
$14$
Work Step by Step
Using the product of the sum and difference of like terms which is given by $(a+b)(a-b)=a^2-b^2,$ the given expression, $
(5-\sqrt{11})(5+\sqrt{11})
,$ is equivalent to
\begin{align*}
&
(5)^2-(\sqrt{11})^2
\\&=
25-11
\\&=
14
.\end{align*}