1、y=ax²+bx+cx=0则y=3=0+0+cc=3把BC代入a+b+3=025a+5b+3=0所以a=3/5b=-18/5y=3x²/5-18x/5+32、显然D是(0,1)或(0,2)设CD是y=kx+bD(0,1),则b=1,过(5,0)0=5k+1k=-1/5D(0,2),则b=2,过(5,0)0=5k+2k=-2/5所以是y=-x/5+1或y=-2x/5+2