(1/x-y+1/x+y)÷xy/x^2-y^2
=[(x+y)/(x^2-y^2)+(x-y)/(x^2-y^2)]×(x^2-y^2)/xy
=(x+y+x-y)/(x^2-y^2)×(x^2-y^2)/xy
=2x/xy
=2/y
2x-6/x-2÷x-3/x^2-4x+4
=2(x-3)/(x-2)×(x-2)^2/(x-3)
=2(x-2)
=2x-4
(1/b-1/a)乘ab/a^2-b^2
=(a-b)/ab×ab/[(a+b)(a-b)]
=1/(a+b)