分类：教育/科学-学习帮助
问题：一道容易的分式题急用要过程 
要过程
回答：[1-(x-y)/(x-3y)]/[(x^2-y^2)/(x^2-6xy+9y^2)]
=[(x-3y)/(x-3y)-(x-y)/(x-3y)]/[(x+y)(x-y)/(x-3y)^2]
=[(x-3y-x+y)/(x-3y)]*(x-3y)^2/(x+y)(x-y)
=-2y(x-3y)/(x+y)(x-y)