1. a,.b.,c dương thỏa mãn a+b+c=1.
CMR: $\frac{1}{ab+2c^{2}+2c}+\frac{1}{bc+2a^{2}+2a}+\frac{1}{ca+2b^{2}+2b}\geq \frac{1}{ab+bc+ac}$
2. a,b,c dương.
CMR: $a^{3}+b^{3}+c^{3}\geq 2abc+\frac{a^{2}+b^{2}+c^{2}}{\frac{1}{a}+\frac{1}{b}+\frac{1}{c}}$
3. a,b,c dương thỏa mãn : a+b+c=3.
CMR: $\frac{a^{2}+bc}{b+ca}+\frac{b^{2}+ca}{c+ab}+\frac{c^{2}+a}{a+bc}\geq 3$