-2 < x ≤ 4
-1 < 0.5x ≤ 2
-2 ≤ -0.5x < 1
-2 + 3 ≤ -0.5x + 3 < 1 + 3
1 ≤ -0.5x + 3 < 4
1 ≤ y < 4
所以y的取值范围是 [1 ,4 )