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

$6\sqrt{3}-3$
Using $a(b+c)=ab+ac$ or the Distributive Property, the given expression, $\sqrt{3}(6-\sqrt{3}) ,$ is equivalent to \begin{array}{l}\require{cancel} 6\sqrt{3}-\sqrt{3(3)} \\\\= 6\sqrt{3}-\sqrt{9} .\end{array} Using the properties of radicals, the expression above simplifies to \begin{array}{l}\require{cancel} 6\sqrt{3}-\sqrt{(3)^2} \\\\= 6\sqrt{3}-3 .\end{array}