A是方程X²+X-1=0的一个根
∴a²+a-1=0
∴a²+a=1
2/（a²-1）-1/（a²-a)
=2/(a+1)(a-1)-1/a(a-1)
=2a/a(a+1)(a-1)-(a+1)/a(a+1)(a-1)
=[2a-(a+1)]/a(a+1)(a-1)
=(a-1)/a(a+1)(a-1)
=1/(a²+a)
=1