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高中数学选择性必修 第二册(381题)



已知\(\left\{ {{a_n}} \right\}\)是等差数列,其前\(n\)项和为\({S_n}\),若\({a_3} + 12{a_7} = {S_{12}}\),则下列判断正确的是(       



A.\({a_9} = 0\)

B.\({S_{17}} = 0\)

C.\({S_6} = {S_{11}}\)

D.\({a_8} \cdot {a_{10}} < 0\)


知识点:第四章 数列


参考答案:ABC


解析:

因为\(\left\{ {{a_n}} \right\}\)是等差数列,\({a_3} + 12{a_7} = {S_{12}}\),所以\({a_1} + 2d + 12\left( {{a_1} + 6d} \right) = 12{a_1} + 66d\)

\({a_1} + 8d = 0\),亦即\({a_9} = 0\)

所以\({S_{17}} = \frac{{\left( {{a_1} + {a_{17}}} \right) \times 17}}{2} = 0,{S_{11}} - {S_6} = {a_7} + {a_8} + {a_9} + {a_{10}} + {a_{11}} = 5{a_9} = 0\)\({a_8} \cdot {a_{10}} = \left( {{a_9} - d} \right) \cdot \left( {{a_9} + d} \right) = a_9^2 - {d^2} = - {d^2} \leqslant 0\)

故选:ABC.

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