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通过数学归纳法证明如果 (a_n) 是公差为 r 的等差数列,那么 a_n = a_1 + (n-1) r 。
通过数学归纳法证明如果 (a_n) 是公差为 r 的等差数列,那么 a_n = a_1 + (n-1) r 。
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