Answer:
(2x - 9)(2x + 9)
Explanation:
4x² - 81
(2x)² - 9²
(2x-9) (2x+9)
4x^2-81
Writing this as
(2x)^2 - 9^2
We recognize this as the difference of squares
a^2 - b^2 = (a-b)(a+b)
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