The equation is:

$x^2 - 4 = 0$

We can solve this by factoring the left-hand side:

$x^2 - 4 = (x - 2)(x + 2) = 0$

Now, set each factor equal to zero:

1. $x - 2 = 0$ gives $x = 2$
2. $x + 2 = 0$ gives $x = -2$

So, the solutions are $x = -2$ and $x = 2$.

The correct answer is:

$\boxed{x = -2 \text{ or } x = 2}$

Would you like more details on how factoring works?

Here are 5 related questions:

1. What is factoring in algebra, and why is it useful?
2. How can you solve quadratic equations using the quadratic formula?
3. What are the solutions to $x^2 - 9 = 0$?
4. What happens when the equation has complex solutions, such as $x^2 + 4 = 0$?
5. Can you solve the equation $x^2 - 4x = 0$?

Tip: Always check if a quadratic equation can be factored before using more advanced methods like the quadratic formula!