约分x-(y-z)^2/(x+y)^2-z^2
问题描述：
约分x-(y-z)^2/(x+y)^2-z^2
答
x-(y-z)^2/(x+y)^2-z^2=(x-y+z)(x+y-z)/(x+y-z)(x+y+z)=(x-y+z)/(x+y+z)
约分x-(y-z)^2/(x+y)^2-z^2
x-(y-z)^2/(x+y)^2-z^2=(x-y+z)(x+y-z)/(x+y-z)(x+y+z)=(x-y+z)/(x+y+z)