The expression 4y^2-1 can be factored using 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 this case, a = 2y and b = 1.

So, 4y^2 - 1 can be factored as (2y + 1)(2y - 1).