Factor X^2-4

$X^{2} - 4$

Rewrite $4$ as $2^{2}$ .

$X^{2} - 2^{2}$

Since both terms are perfect squares, factor using the difference of squares formula, $a^{2} - b^{2} = (a + b) (a - b)$ where $a = X$ and $b = 2$ .

$(X + 2) (X - 2)$