y2=kx+b的图像过A(-2,4)B(8,2)
则k=(4-2)/(-2-8)=-1/5, b=y-kx=4+1/5*(-2)=18/5
故y1=ax^2+18x/5+c
代入A得:4=4a-36/5+c
代入B得; 2=64a+144/5+c
两式相减得:a=-19/30
所以y1开口向下,y2斜率为负.由此得y1>y2的取值范围是-2
y2=kx+b的图像过A(-2,4)B(8,2)
则k=(4-2)/(-2-8)=-1/5, b=y-kx=4+1/5*(-2)=18/5
故y1=ax^2+18x/5+c
代入A得:4=4a-36/5+c
代入B得; 2=64a+144/5+c
两式相减得:a=-19/30
所以y1开口向下,y2斜率为负.由此得y1>y2的取值范围是-2