（a^2-b^2)/ab-(ab-b^2)/(ab-a^2)
=（a^2-b^2)/ab-b(a-b)/a(b-a)
=（a^2-b^2)/ab-(-b)/a
=（a^2-b^2)/ab+b/a
=（a^2-b^2)/ab+b^2/ab
=（a^2-b^2+b^2)/ab
=a^2/ab
=a/b
x/(x^2-y^2)-y/(x^2+2xy+y^2)
=x/[(x+y)(x-y)]-y/(x+y)^2
=x(x+y)/[(x+y)^2(x-y)]-y(x-y)/[(x+y)^2(x-y)]
=(x^2+xy-yx+y^2)/[(x+y)^2(x-y)]
=(x^2+y^2)/[(x+y)^2(x-y)]
这个不会看不懂吧