[(x+2/x^2-2x) - (x-1/x^2-4x+4)]÷x-4/x
=[(x+2)/x(x-2)]-[(x-1)/(x-2)^2]÷(x-4)/x
={[(x^2-4)-x(x-1)]/[x(x-2)^2]}×[x/(x-4)]
={[(x-4)/[x(x-2)^2]}×[x/(x-4)]
=1/(x-2)^2
当x=2+根号3时,
原式=1/(√3)^2
=1/3