Question

Factor completely: 16x2 − 81

Answer 1

Difference of squares. I see.
16x^2 - 9^2
(16x + 9)(16x - 9)

Answer 2

Because:

\(\Large \color{Black}{\Rightarrow a^2 - b^2 = (a + b)(a -b) }\)

Answer 3

Actually (4x + 9)(4x - 9)
My mistake.