Factor x^2-81=0

$x^{2} - 81 = 0$

Step 1

Rewrite $81$ as $9^{2}$ .

$x^{2} - 9^{2} = 0$

Step 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 $b = 9$ .

$(x + 9) (x - 9) = 0$