y=-x2+4x+3(-3

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y=-x2+4x+3(-3y=-x2+4x+3(-3y=-x2+4x+3(-3y=-(x2-4x+4)+7=-(x-2)^2+7又（-3ymin=-(-3-2)^2+7=7-25=-18ymax=-(

y=-x2+4x+3(-3
y=-x2+4x+3(-3<=x<=1)求值域

y=-x2+4x+3(-3
y=-(x2-4x+4)+7
=-(x-2)^2+7
又（-3<=x<=1)
ymin=-(-3-2)^2+7=7-25=-18
ymax=-(1-2)^2+7=6
所以值域为[-18,6]