1.3ab分之a²-4b²×a-2b分之ab 2.a²-4a+4分之a-1÷a²

1.3ab分之a²-4b²×a-2b分之ab
=(a+2b)(a-2b)/3ab ×ab/(a-2b)
=(a+2b)/3

2.a²-4a+4分之a-1÷a²-4分之a平方-1
=(a-1)/(a-2)² ×(a+2)(a-2)/(a+1)(a-1)
=(a+2)/(a-2)(a+1)

3.a²+ab分之a-b÷a²b²-a的四次方分之ab-a平方
=(a-b)/a(a+b) ×a²(a+b)(a-b)/a(b-a)
=-(a-b)
=b-a
4.（xy-x²）÷xy分之x-y
=-x(x-y)×xy/(x-y)
=-x²y