x²-2x/x÷(x-4/x)
=x(x-2)/x×x/(x+2)(x-2)
=x/(x+2)
当x=3时 原式=3/(3+2)=3/5
(1+1/x-2)÷x²-2x+1/x²-4
=(x-1)/(x-2)×(x+2)(x-2)/(x-1)²
=(x+2)/(x-1)
当x=-5时
原式=-3/(-6)=1/2
[1+2x-4/(x+1)(x-2)]÷x+3/x²-1
=(x+3)/(x+1)×(x+1)(x-1)/(x+3)
=x-1
当x=6时
原式=6-1=5