factor

25u^2-81

25u^2 - 81

This is a difference of two squares. Therefore, the factor is
(5u - 9)(5u + 9)

hope this helps :3

To factor the expression 25u^2 - 81, we can use the difference of squares formula. The difference of squares formula states that a^2 - b^2 can be factored as (a + b)(a - b).

In our expression, we have 25u^2 - 81. We can rewrite 25u^2 as (5u)^2 and 81 as 9^2.

So, applying the difference of squares formula, we can factor 25u^2 - 81 as follows:

(5u + 9)(5u - 9)

And that is the factored form of the expression 25u^2 - 81.