∵x=1/x ∴x平方=1
(x4+x2-6)/(x2+3)=[(x2)2+1-6]/4=(1+1-6)/4=-1
x4-x2-x+1=x(x3-1)-(x2-1)
=x(x-1)(x2+x+1)-(x-1)(x+1)
=(x-1)(x3+x2+x-x-1)
=(x-1)(x3+x2-1)