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