Question

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

Answer 1

`(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