Answer:
x^4 - 81 = 0
(x² - 9)(x² + 9) = 0
Notice that the first of these is itself a difference of two squares:
(x - 3)(x + 3)(x² + 9) = 0
So the solutions are x = 3, x = -3, x = 3i, x = -3i
The factor is x-6 since the two factors of your equation are (6x-6) and (x-6)
