Answer:
Step-by-step explanation:
Identity used: [tex]a^{2}-b^{2} = (a + b)(a -b)[/tex]
81 = 9*9 = 9²
a = x^2 and b =9
Then again 9 = 3*3.In this way, (x² - 9 ) can be again factored
[tex]x^{4} - 81 = (x^{2})^{2}-9^{2}\\\\=(x^{2} + 9)(x^{2} - 9)\\\\=(x^{2}+9) (x^{2} -3^{2})\\\\= (x^{2} + 9}(x+3)(x-3)[/tex]
