Chứng minh rằng: C = 1/10 + 1/11 + 1/12 + ... + 1/99 + 1/100 > 1

* Hướng dẫn giải

$C=\frac{1}{10}+\left(\frac{1}{11}+\mathrm{...}+\frac{1}{100}\right)>\frac{1}{10}+\underset{90so}{\underbrace{\left(\frac{1}{100}=\mathrm{...}+\frac{1}{100}\right)}}=\frac{1}{10}+\frac{90}{100}=1$