x^8 + 6x^4 + 25 = x^8 + 10x^4 + 25 - 4x^4 = (x^4 + 5)^2 - (2x^2)^2 =
(x^4 + 2x^2 + 5) * (x^4 - 2x^2 + 5)
x^8 + 6x^4 + 25 = x^8 + 10x^4 + 25 - 4x^4 = (x^4 + 5)^2 - (2x^2)^2 =
(x^4 + 2x^2 + 5) * (x^4 - 2x^2 + 5)