Cho $x_{i}$ >0(mọi i,$n\epsilon N,n\geq 3)$.CMR:
$\frac{x_{1}}{x_{2}+x_{3}}+\frac{x_{2}}{x_{3}+x_{4}}+...+\frac{x_{n}}{x_{1}+x_{2}}\geq \frac{3n}{4}-\frac{1}{4}(\frac{x_{2}}{x_{1}}+\frac{x_{3}}{x_{2}}+...+\frac{x_{n}}{x_{n-1}}+\frac{x_{1}}{x_{n}})$
Edited by stronger steps 99, 06-08-2013 - 08:42.
Do not worry about your difficulties in Mathematics. I can assure you mine are still greater. 
