y=-x²+4x-4+5=-(x-2)²+5开口向下，对称轴x=2x=2,y=5x=0,y=1值域[1,5]
y=-x²+4x+1 =-(x²-4x+4)+5 =-(x-2)²+50≤x≤3∴-4≤-(x-2)²≤01≤y≤5
