（m-1）x²+2mx+2x+m+3=0
（m-1）x²+2(m+1)x+m+3=0
(1) m-1=0,m=1
4x+4=0
x=-1
(2) m≠1
m-1 m+3
1 1
[(m-1)x+m+3](x+1)=0
x1=-1
x2=-(m+3)/(m-1)确定对么