Answer
$146$
Work Step by Step
Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms and using $i^2=-1$, the given expression $
(5-11i)(5+11i)
,$ simplifies to
\begin{array}{l}\require{cancel}
(5)^2-(11i)^2
\\\\=
25-121i^2
\\\\=
25-121(-1)
\\\\=
25+121
\\\\=
146
.\end{array}