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

[ 1/1Inequality]
    Assignment:Find the solution set of inequality 2×（r－21）×r ≤－3 .
    Question type: Inequality
    Solution:
    The inequality can be reduced to 1 inequality：
        2 × ( r - 21 ) × r ≤ -3         (1)

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    From inequality(1)：
         0.071673 ≤ r ≤ 20.928327

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    The final solution set is :
         0.071673 ≤ r ≤ 20.928327

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