解y=-2(x+1)²-3开口向下,x=-1,顶点(-1,-3)y=-3x²-4x+7=-3(x²+4/3x)+7=-3(x²+4/3x+4/9)+4/3+7=-3(x+2/3)²+25/7开口向下,对称轴x=-2/3顶点(-2/3,25/7)y=3/4(x²-1)=3/4x²-3/4当x=0...