Simplify the following:

(2x - y + 3)(2x - y - 3)

(2x - y + 3)(2x - y - 3)

Let (2x - y) = a

Then, the given expression = (a+3)(a-3) = (a)² - (3)²

= a² - 9 = (2x-y)² - 9 = (2x)² - 2(2x)(y) + y² - 9

= 4x² - 4xy + y² - 9