1. Chứng minh rằng $1 + \frac{1}{\sqrt{2}} + \frac{1}{\sqrt{3}} + \frac{1}{\sqrt{4}} + ... + \frac{1}{\sqrt{2004}} + \frac{1}{\sqrt{2005}} > 2\sqrt{2006}$
2. Chứng minh rằng B = $\frac{1}{2} + \frac{1}{3\sqrt{2}} + \frac{1}{4\sqrt{3}} + \frac{1}{5\sqrt{4}} + ... + \frac{1}{2005\sqrt{2004}} + \frac{1}{2006\sqrt{2005}} < 2$
Edited by Quoc Tuan Qbdh, 19-12-2015 - 19:54.