Question

16x² - 8y²

Explanation:

Step1: Identify difference of squares

Recognize $16x^2=(4x)^2$, $81y^2=(9y)^2$

Step2: Apply difference of squares formula

Use $a^2-b^2=(a-b)(a+b)$
$$16x^2-81y^2=(4x)^2-(9y)^2=(4x-9y)(4x+9y)$$

Answer:

$(4x-9y)(4x+9y)$