Answer:
(9x + 2)(9x - 2)
Step-by-step explanation:
To factor this expression, you can use a neat trick called difference of squares.
Difference of squares tells us:
a^2-b^2 = (a+b)(a-b)
Now look at the expression we have here:
81x^2 - 4
well, we know that 81 is 9^2, x^2 is literally x^2, and 4 is 2^2
So we can rewrite this as:
(9x)^2 - 2^2
By difference of squares that gives us:
(9x + 2)(9x - 2)
