Draw the graph of the function, and you can see that the left side of the parabola gradually increases and the right side gradually decreases.

(1) When x ≤- 2, the function has a maximum value of 3.

(2) When x≤2, the maximum value of the function is, and when x=- 1, the maximum value is 4.

(3) When -2≤x≤ 1, the function has a maximum and a minimum.

When x=- 1, the maximum value is 4, and when x= 1, the minimum value is 0.

(4) When 0≤x≤3, the function has a maximum and a minimum.

When x=0, the maximum value is 3; when x=3, the minimum value is-12.

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