1.a²-a=0,a=0,1
(a-1)/(a+2)*(a²-4)/(a²-2a+1)÷1/(a²-1)=(a-1)/(a+2)*(a-2)(a+2)/(a-1)²÷1/[(a-1)(a+1)]=(a-1)(a-2)(a+1)
a=0,原式=-2,
a=1,原式=0
2.原式=(x²-3x)/(x²-1)+(2x-1)(x+1)/(x-1)(x+1)