Answer
$7$
Work Step by Step
Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, the expression $
(\sqrt{6}+i)(\sqrt{6}-i)
$ simplifies to
\begin{array}{l}
(\sqrt{6})^2-(i)^2
\\=
6-i^2
\\=
6-(-1)
\\=
7
.\end{array}