-y - y/1-y +1
问题描述：
-y - y/1-y +1
答
-y-y/(1-y)+1
=(y²-y-y+1-y)/(1-y)
=(y²-3y+1)/(1-y)
答
原式=[-y(y-1)-y+(1-y)]/(1-y)
=(-y²+y-y+1-y)/(1-y)
=(-y²-y+1)/(1-y)