a^2-a-1=0
a²=a+1
原式=[(a-1)(a+1)/a(a+1)-a(a-2)/a(a+1)]×(a+1)²/a(2a-1)
=(a-1+a²+2a)/a(a+1)×(a+1)²/a(2a-1)
=(a+1)/a²
=(a+1)/(a+1)
=1