GRE
The average (arithmetic mean) of $$s$$, $$t$$, $$u$$, $$\frac{1}{s}$$, $$\frac{1}{t}$$, and $$\frac{1}{u}$$
$$1$$
$$b_{n}$$
$$\frac{-1}{n^2-n}$$
25000 +道题目
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