Chapter 7 - Section 7.2 - Rational Exponents - Exercise Set - Page 425: 65

$4x^{2/3}-9$

Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, then, \begin{array}{l} (2x^{1/3}+3)(2x^{1/3}-3) \\\\= (2x^{1/3})^2-(3)^2 \\\\= 2^2x^{\frac{1}{3}\cdot2}-9 \\\\= 4x^{2/3}-9 .\end{array}