（1）原式=

a-2

a2

×

a-1

(a-2)2

×

a

a-1

=

1

a(a-2)

；

（2）原式=

4xy+(x-y)2

x-y

×

4xy-(x+y)2

x+y

=

(x+y)2

x-y

×

-(x-y)2

x+y

=-（x+y）（x-y）=-x²+y²．