[(x+2)/(x^2-2x)-(x-1)/(x^2-4x+4)]÷[(4-x)/x]
=[(x+2)/x(x-2)-(x-1)/(x-2)²]÷[(4-x)/x]
=[(x+2)(x-2)-x(x-1)]/x(x-2)²÷[(4-x)/x]
=[(x-4)/x(x-2)²]*[x/(4-x)]
=-1/(x-2)²
当x=-3时,原式=-1/(-3-2)²=-1/25