Cho \[A = 1 - \frac{1}{2} + \frac{1}{3} - \frac{1}{4} + \frac{1}{5} - \frac{1}{6} + ... + \frac{1} - \frac{1}\]. Chứng minh \[A < \frac{5}{6}\]
Cho \[A = 1 - \frac{1}{2} + \frac{1}{3} - \frac{1}{4} + \frac{1}{5} - \frac{1}{6} + ... + \frac{1} - \frac{1}\]. Chứng minh \[A < \frac{5}{6}\]