不经过第3象限
则对称轴x=-(1-2m)/2>=0
m>=1/2
且y轴的截距
即x=0时,y>=0
则-m+5>=0
m但答案上说是大于等于-2分之更号19，小于等于5？哦，对不起分两种△>=01-4m+4m²+4m-20>0m²<19/4m<-√19/2,m>√19/2此时要满足对称轴x=-(1-2m)/2>=0m>=1/2且y轴的截距即x=0时，y>=0则-m+5>=0m<=5所以√19/2=m<=5△<=0则-√19/2<=m<=√19/2此时图像在x轴上方，肯定不过第三象限综上-√19/2<=m<=5