（x-y/x+2y)/(x^2-y^2/x^2+4xy+4y^2)先化简后求值 其中x=-2,y=3
问题描述：
（x-y/x+2y)/(x^2-y^2/x^2+4xy+4y^2)先化简后求值 其中x=-2,y=3
答
（x-y/x+2y)/(x^2-y^2/x^2+4xy+4y^2)
=（x-y/x+2y)/(x-y)(x+y)/(x+2y)^2
=1/(x+y)/(x+2y)
=(x+2y)/(x+y)
代入
=4