x^2-1分之1-x^2
=(x²-1)/-(x²-1)
=-1
( 2 )x^2-(y-z)^2分之(x+y)^2-z^2
=（x+y+z）（x+y-z）/(x+y-z)(x-y+z)
=(x+y+z)/(z-y+z)
如果本题有什么不明白可以追问,