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答案:107 2,5,8,……,212是首項為2,公差為3的等差數列, 所以,通項公式an=2+(n-1)*3 所以,212是71項, 所以,此等差數列前71項和為Sn=(2+212)*71/2 所以,所求平均數為Sn/71=(2+212)/2=107
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