y=3(x²+2x/3)=3(x²+2x/3+1/9-1/9)=3(x²+2x/3+1/9)-1/3=3(x+1/3)²-1/3所以开口向上对称轴是x=-1/3顶点(-1/3,-1/3)有最小值-1/3y=-3x²+6x-2=-3(x^2-2x+1)+1=-3(x-1)^2+1,抛物线,开口向下,对...