Answer:

(9m + 2n)(9m - 2n)

Step-by-step explanation:

Formula of difference of two squares

x² - y² = (x + y)(x - y)

To help you recognize the difference of two squares, consider the following:

• There must be two terms that are both perfect squares.

• One of the two terms is negative.

• Thus, the difference of two squares can be express as x² - y²

Example: 81m² - 4n²

Since we know the square root of 81 is 9 and the square root of 4 is 2, we can rewrite the expression as:

9²m² - 2²n²

Now apply the formula

x² - y² = (x + y)(x - y)

Therefore,

9²m² - 2²n² = (9m + 2n)(9m - 2n)