factor 25-81z^2

(a^2 - b^2) -(a-b)(a+b)

To factor the expression 25 - 81z^2, we can use the difference of squares formula. The formula is a^2 - b^2 = (a + b)(a - b), which is useful here because 25 can be written as 5^2 and 81z^2 can be written as (9z)^2.

Now, let's rewrite the expression using the difference of squares formula:

25 - 81z^2 = (5)^2 - (9z)^2

Using the difference of squares formula, we can factor this as:

(5 - 9z)(5 + 9z)

So the factored form of 25 - 81z^2 is (5 - 9z)(5 + 9z).