The expression to factor is $9y^2 - 4$. This is a difference of squares, which factors using the formula:

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

Here:

• $a^2 = 9y^2$, so $a = 3y$,
• $b^2 = 4$, so $b = 2$.

Applying the formula: $9y^2 - 4 = (3y - 2)(3y + 2)$

Final Answer:

$(3y - 2)(3y + 2)$

Would you like further explanation? Here are some related questions:

1. What is the general method for factoring a difference of squares?
2. How do you identify if an expression is a difference of squares?
3. Can the formula $a^2 - b^2 = (a - b)(a + b)$ be extended to higher powers?
4. What happens if $9y^2 + 4$ is given instead? How would you approach factoring that?
5. Can you derive the difference of squares formula from first principles?

Tip: Always check if an expression is a perfect square on both terms to apply the difference of squares rule effectively.