-2=-k+b-4=2k+b相减，得3k=-2k=-2/3b=-2+k=-2-2/3=-8/3y=-2/3x-8/3(2) x=0,y=-8/3与y轴交点：(0,-8/3)y=02/3x=-8/3x=-4与x轴交点：(-4,0)
