(2y+1）²+3(2y+1)+2=0
（2y+1+1)(2y+1+2)=0
(2y+2)(2y+3)=0
y=-1y=-1.5（2y+1+1)(2y+1+2)=0怎么得出来的？十字相乘法啊1 +21 +1