How do you factor x^4-8x^2-9?

1 Answer

(x^2+1)(x+3)(x-3)

Explanation:

first lets substitute x^2 = t
we get t^2 - 8*t - 9
now split the middle term t^2 + t - 9*t - 9
factorize now t(t+1) -9(t+1)
now we get (t+1)(t-9)
now substitute back t=x^2
we get (x^2+1)(x^2-9)
we can still factorize the x^2-9 term
so we get (x^2+1)(x+3)(x-3)
this is the answer