## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$-4$
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, $(\sqrt{5}+3)(\sqrt{5}-3) ,$ is equivalent to \begin{array}{l}\require{cancel} (\sqrt{5}+3)(\sqrt{5}-3) \\\\= (\sqrt{5})^2-(3)^2 \\\\= 5-9 \\\\= -4 .\end{array}