2分之1(y-1)的平方+2y(y-1)=0
(y-1)²+4y(y-1)=0(两边同乘以2)
(y-1)(y-1+4y)=0
(y-1)(5y-1)=0
所以y-1=0 y=1
或者5y-1=0 y=1/5