Answer
$29$
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 is equivalent to
\begin{array}{l}\require{cancel}
(2+5i)(2-5i)
\\\\=
(2)^2-(5i)^2
\\\\=
4-25i^2
.\end{array}
Using $i^2=-1,$ the expression above is equivalent to
\begin{array}{l}\require{cancel}
4-25i^2
\\\\=
4-25(-1)
\\\\=
4+25
\\\\=
29
.\end{array}
