[tex]\begin{gathered} x^4-81\text{ (Difference of squares)} \\ \sqrt[]{x^4}=x^2\text{ (Taking the square root)} \\ \sqrt[]{81^{}}=9\text{ (Taking the square root)} \\ (x^2+9)(x^2-9)\text{ (Factoring the difference of squares)} \\ \text{The answer is }(x^2+9)(x^2-9) \end{gathered}[/tex]
