Question

1. factor. $x^2 - 81$

Explanation:

Step1: Recognize difference of squares

$x^2 - 81 = x^2 - 9^2$

Step2: Apply difference of squares formula

Recall $a^2 - b^2 = (a-b)(a+b)$, so substitute $a=x$, $b=9$:
$x^2 - 9^2 = (x-9)(x+9)$

Answer:

$(x - 9)(x + 9)$