![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
Cho [imath]a_1,a_2,...,a_n[/imath] là các số thực dương thỏa mãn [imath]a_1a_2...a_n=1[/imath]. Chứng minh rằng:
[math]\dfrac{1}{a_1}+\dfrac{1}{a_2}+...+\dfrac{1}{a_n}+\dfrac{3n}{a_1+a_2+...+a_n}\geq n+3 ;\forall n\geq 4[/math]
[math]\dfrac{1}{a_1}+\dfrac{1}{a_2}+...+\dfrac{1}{a_n}+\dfrac{3n}{a_1+a_2+...+a_n}\geq n+3 ;\forall n\geq 4[/math]