Factor $x^{2}-81$

Step 1 ：Factor the expression $x^{2}-81$

Step 2 ：Recognize this as a difference of squares problem. The difference of squares formula is $a^{2} - b^{2} = (a - b)(a + b)$

Step 3 ：In this case, $a = x$ and $b = 9$ because $9^{2} = 81$

Step 4 ：Rewrite $x^{2} - 81$ as $(x - 9)(x + 9)$

Step 5 ：The factored form of $x^{2}-81$ is \(\boxed{(x - 9)(x + 9)}\)