y=-x²+6x-1
=-(x²-6x)-1
=-[(x²-6x+9)-9]-1
=-[(x-3)²-9]-1
=-(x-3)²+9-1
=-(x-3)²+8
函数图像的开口向下,
对称轴是直线X=3,
顶点坐标是(3,8).