Respuesta :

16x² - 81
This equation is in difference of square form.
we know that if it is difference of square then our answer should look like 
( x+y) ( x-y)
According To Question
16x² - 81
(4x - 9) { because 4 *4 = 16 and 9 * 9 = 81 }
(4x - 9) ( 4x + 9) is our answer

Hope this helps.. :)
Exvited
[tex]16x^2 - 81 \\ \\ (4x)^2 - 9^2 \\ \\ (4x + 9)(4x - 9) \\ \\ [/tex]

The answer is: (4x + 9)(4x - 9).