等比数列前n项和为Sn,有人算得S1="8," S2="20," S3="3

问题选择题

等比数列前n项和为S_n,有人算得S₁="8," S₂="20," S₃="36," S₄=65,后来发现有一个数算错了，错误的是（）

A．S₁

B．S₂

C．S₃

D．S₄

答案

答案：C

题目分析：根据题意，由于等比数列前n项和为S_n,有人算得S₁="8," S₂="20," S₃=36，如果S₁="8," S₂- S₁=12，，故S₃="38," S₄=65成立，故可知错误的是S₃，选C.

点评：解决的关键是根据等比数列前几项来确定正确性，属于基础题。