1. Cho $a, b, c>0$. Chứng minh:a) $a+b+c\leq \frac{a^{2}+b^{2}}{2c}+\frac{b^{2}+c^{2}}{2a}+\frac{c^{2}+a^{2}}{2b}\leq \frac{a^{3}}{bc}+\frac{b^{3}}{ca}+\frac{c^{3}}{ab}$
b) $\frac{a^{8}+b^{8}+c^{8}}{a^{3}b^{3}c^{3}}\geq \frac{1}{a}+\frac{1}{b}+\frac{1}{c}$