y=3(x²-bx/3+b²/36-b²/36)+4=3(x-b/6)²-b²/12+4顶点(b/6,-b²/12+4)顶点在x轴上即纵坐标为0-b²/12+4=0b²=48b=-4√3,b=4√3顶点y轴上即顶点横坐标跑是0b/6=0b=0...