原式=[1-1/(x+2)]÷[(x²+2x+1)/(x²-4)]
=[(x+2)/(x+2)-1/(x+2)]÷{(x+1)²/[(x+2)(x-2)]}
=[(x+1)/(x+2)]×[(x+2)(x-2)/(x+1)²]
=(x-2)/(x+1)