(x^2 - 9) and (x^2 + 9) are factors of x^4 - 81
We can verify this by multiplying them.
(x^2 - 9)(x^2 + 9)
x^4 + 9x^2 - 9x^2 - 81
x^4 - 81
When we have a binomial with two perfect squares, we can use this equation:
[tex]a^2 - b^2 = (a - b)(a + b)[/tex]
