[x²-(y-z)²]/[(x+y)²-z²]
=[x-(y-z)][x+(y-z)]/[(x+y+z)(x+y-z)]
=(x+z-y)(x+y-z)/[(x+y-z)(x+y+z)]
=(x+z-y)/(x+y+z)
=(x+y+z)分之（x+z-y)
望采纳