y²+3y-2=0
y²+3y+(3/2)²-（3/2）²-2=0
[y+(3/2)]²-17/4=0
[y+(3/2)]²=17/4
y+(3/2)=±v17/2
则y1=-(3/2)+v17/2 y2=-(3/2)-v17/2