Answer:
![(x^2-9)(x^2+9)\\(x-3)(x+3)(x^2+9)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/9qipo4h05dvmccbjskx0f4l3gjh86kvmz0.png)
Explanation:
To factor the expression, factor as a difference of squares. Find the square root of each term and write it in this form (x+a)(x-a).
![x^4 - 81\\(x^2 - 9)(x^2 + 9)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/1wzrsxq3hbd30sata168d5g4fjbkln43q6.png)
Factor x² - 9 as a difference of squares.
![(x^2-9)(x^2+9)\\(x-3)(x+3)(x^2+9)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/9qipo4h05dvmccbjskx0f4l3gjh86kvmz0.png)
This is the most factored form because a sum of squares cannot be factored.