原式
=[(a+2)/a(a-2)-8/(a+2)(a-2)]×[a/(a-2)]
={[(a+2)²-8a]/a(a+2)(a-2)]}×[a/(a-2)]
=[(a²+4a+4-8a)/a(a+2)(a-2)]×[a/(a-2)]
=[(a²-4a+4)/a(a+2)(a-2)]×[a/(a-2)]
=[(a-2)²/a(a+2)(a-2)]×[a/(a-2)]
=a(a-2)²/[a(a+2)(a-2)(a-2)]
=1/(a+2)