#### Answer

$1$

#### 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 the properties of radicals, the given expression, $
(2-\sqrt{3})(2+\sqrt{3})
,$ is equivalent to
\begin{array}{l}\require{cancel}
2^2-(\sqrt{3})^2
\\\\=
4-3
\\\\=
1
.\end{array}