y=-x^2+6x+1=-(x-3)^2+10
开口向下,对称轴是X=3,顶点坐标是(3,10)
y=-2x^2+8x-8=-2(x^2-4x+4)=-2(x-2)^2
开口向下,对称轴是X=2,顶点坐标是(2,0)