Question

Why is the completely factored form X^4+8x^2-9

Answer 1

Greetings!

This is still factor-able:
$x^4+8x^2-9$
$x^4+9x^2-x^2-9$
Factor by grouping.
$x^2(x^2+9)-1(x^2+9)$
$(x^2+9)(x^2-1)$
Factor by difference in squares.
$(x^2+9)(x-1)(x+1)$

Hope this helps.
-Benjamin