Question 883719
X is a misprint.  

Starting from {{{x^4-x^2-20}}} try conveniently substituting like {{{u=x^2}}} and rewrite the expression as {{{u^2-u-20}}}.  You can take your guesses using 5 and 4 and hopefully find  {{{(u+4)(u-5)}}}, and this obviously works  ----- the expression using u.


Now substitute back for u:
{{{highlight((x^2+4)(x^2-5))}}}.
The answer key is wrong.
YOUR first result was correct.