factor.

Question

x^4-81=0

*difference of squares not sure where to start

Answer 1

start by recalling that
a^2 - b^2 = (a-b)(a+b) and do it twice in this case
x^4 - 81
= (x^2-9)(x^2+9)
= (x-3)(x+3)(x^2+9)

Answer 2

ty!!