数学试题讲解

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已知

{a_{n}}

为等差数列,

S_{n}

为其前

n

项和, 则下列结论一定成立的是

A. 若

a_{1} = a_{5}

, 则

a_{1} = a_{2} = \dots = a_{n}

B. 若

a_{5} > a_{3}

, 则

S_{1} < S_{2} < \dots < S_{n}

C. 若

a_{3} = 2

, 则

a_{1}^{2} + a_{5}^{2} ⩾ 8

D. 若

a_{4} = 8, a_{8} = 4

, 则

S_{12} = 66