(y-1)(y+2)=2y(1-y)
(y-1)(y+2)－2y(1-y)=0
(y-1)(y+2)＋2y(y－1)=0
(y－1)(y＋2＋2y)=0
(y－1)(3y＋2)=0
所以y－1=0 y=1
或者3y＋2=0 y=﹣2／3