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

[ 1/1Inequality]
    Assignment:Find the solution set of inequality (21+d)(21+4d) <(21+11d） .
    Question type: Inequality
    Solution:
    The inequality can be reduced to 1 inequality：
         ( 21 + d ) * ( 21 + 4 * d ) < ( 21 + 11 * d )         (1)

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    From inequality(1)：
         -35/2 < d < -6

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    The final solution set is :
         -35/2 < d < -6

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