Chapter 8 - Polynomials and Factoring - 8-4 Multiplying Special Cases - Practice and Problem-Solving Exercises - Page 496: 46

$4g^{2} - 81h^{2}$

We use the formula for the difference of squares to apply to this question. The difference of squares formula is: $(a-b) (a+b) = a^{2} - b^{2}$ In the given formula let 2g represents a and 9h represents b. $(2g-9h) (2g+9h) = (2g)^{2} - (9h)^{2}$ = $4g^{2} - 81h^{2}$