Answer
$(4x^{2}-5)(x-1)(x+1)$
Work Step by Step
$4x^{4}-9x^{2}+5$
... Searching for two factors of $ac=20$ whose sum is $b=-9,$
we find$\qquad-4$ and $-5.$
Rewrite the middle term and factor in pairs:
$=4x^{4}-4x^{2}-5x^{2}+5=$
$=4x^{2}(x^{2}-1)-5(x^{2}-1)$
$=(4x^{2}-5)(x^{2}-1)\qquad$...recognize the difference of two squares: $a^{2}-b^{2}=(a-b)(a+b)$
=$(4x^{2}-5)(x-1)(x+1)$
