Chứng tỏ rằng \(\frac{1}{{101}} + \frac{1}{{102}} + ... + \frac{1}{{299}} + \frac{1}{{300}} > \frac{2}{3}\)
Ta có:
\(\begin{array}{l}
\frac{1}{{101}} > \frac{1}{{300}}\\
\frac{1}{{102}} > \frac{1}{{300}}\\
...\\
\frac{1}{{299}} > \frac{1}{{300}}\\
\Rightarrow \underbrace {\frac{1}{{101}} + \frac{1}{{102}} + ... + \frac{1}{{299}} + \frac{1}{{300}}}_{200P/S}\\
> \frac{1}{{300}}.200 = \frac{2}{3}
\end{array}\)
-- Mod Toán 6
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