先化简，再求值： （1+1/x-2）÷x^2-2x+1/x^2-4,其中x=-5 =（x-2+1）/(x-2)×(x+2)(x-2)/(x-1)² =(x+2)/(x-1) =(-5+2)/(-5-1) =-3/(-6) =1/2
