y1=6-x, y2=2+7x,要使y1比y2小-3则6-x+3=2+7x解得x=7/8
Y1-Y2=3,Y1=6-X.Y2=2+7X.解得X=1/8,Y1=47/8,Y2=23/8
y1=6-x, y2=2+7x , y1=y2-3 6-x=2+7x+3 => 8x=1 => x= 1/8
X=7/8