Gaokao Math Practice Question
6. (5 分) 设首项为 1 , 公比为 $\frac{2}{3}$ 的等比数列 $\left\{a_{n}\right\}$ 的前 $n$ 项和为 $S_{n}$, 则 ( )
- A.$S_{n}=2 a_{n}-1$
- B.$S_{n}=3 a_{n}-2$
- C.$S_{n}=4-3 a_{n}$
- D.$S_{n}=3-2 a_{n}$
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