Question 9384
X^4 + (1/X^4)  = (X^2 - (1/X^2))^2 + 2 

But we know X^4 + (1/X^4) = 731  

So  731 =  (X^2 - (1/X^2))^2 + 2 

or  (X^2 - (1/X^2))^2 = 731 - 2 

= (X^2 - (1/X^2))^2 = 729
 
=  (X^2 - (1/X^2)) = 27