先化简再求值：a²b+ab²分之a²-b²÷（2ab分之a²+b

原式=(a+b)(a-b)/ab(a+b)÷(a²+b²-2ab)/2ab
=(a-b)/ab×2ab/(a-b)²
=2/(a-b)
=2/(3+√5-3+√5)
=√5/5