Overview: 1 questions will be solved this time.Among them
           ☆1 inequalities

[ 1/1Inequality]
    Assignment:Find the solution set of inequality -2 ≤4/a ≤-1 .
    Question type: Inequality
    Solution:
    The inequality can be reduced to 2 inequalities：
        -2 ≤4 / a         (1)
        4 / a ≤ -1         (2)
        From the definition field of divisor
        x ≠ 0        (3 )

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    From inequality(1)：
         a ≤ -2 或  a ≥ 0
    From inequality(2)：
         -4 ≤ a ≤ 0
    From inequality(3)：
         a < 0 或  a ＞ 0

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    From inequalities (1) and (2)
         -4 ≤ a ≤ -2 或  0 ≤ a ≤ 0    (4)
    From inequalities (3) and (4)
         -4 ≤ a ≤ -2    (5)

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    The final solution set is :
         -4 ≤ a ≤ -2

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