原式=[(x-2)(x+4)/x(x+1)(x+2)]÷[(x-2)(x+4)/x(x+1)]
=[(x-2)(x+4)/x(x+1)²]÷[(x-2)(x+4)/x(x+1)]
=[1/(x+1)]×[(x-2)(x+4)/x(x+1)]÷[(x-2)(x+4)/x(x+1)]
=1/(x+1)