原式=(a-1)²/(a+1)(a-1)+2a(a-2)/(a+1)(a-2)
=(a-1)/(a+1)+2a/(a+1)
=(3a-1)/(a+1)
=(√3-1)/(√3/3+1)
=3(√3-1)/(3+√3)
=2√3-3