yx^2+3yx+6y=x+2
yx^2+(3y-1)x+(6y-2)=0
这里x是实数,所以方程有实数根
所以判别式大于等于0
所以9y^2-6y+1-24y^2+8y>=0
15y^2-2y-1<=0
(5y+1)(3y-1)<=0
-1/5<=y<=1/3
值域[-1/5,1/3]