$ \frac{a^3+b^3}{2ab}\geq \frac{(a+b)(a^2+b^2-ab)}{2ab}\geq \frac{(a+b)(2ab-ab)}{2ab}=\frac{(a+b)ab}{2ab}=\frac{(a+b)}{2}$Tương tự => đpcm
$ \frac{a^3+b^3}{2ab}
= \frac{(a+b)(a^2+b^2-ab)}{2ab}\geq \frac{(a+b)(2ab-ab)}{2ab}=\frac{(a+b)ab}{2ab}=\frac{(a+b)}{2}$Tương tự => đpcm