cho $a,b,c,d>0$
cmr $\frac{a^2}{b+c+d}+\frac{b^2}{a+c+d}+\frac{c^2}{a+b+d}+\frac{d^2}{a+b+c}\geq \frac{4}{3}$
2. cho a, b, c>0
cmr $\frac{bc}{a^2b+a^2}+\frac{ab}{ac^2+bc^2}+\frac{ac}{ab^2+b^2c}\geq \frac{1}{2a}+\frac{1}{2b}+\frac{1}{2c}$
3. Cho a, b, c>0
và $12(\frac{1}{a^2}+\frac{1}{b^2}+\frac{1}{c^2})=3+\frac{1}{a}+\frac{1}{b}+\frac{1}{c}$
CMR: $\frac{1}{4a+b+c}+\frac{1}{a+4b+c}+\frac{1}{a+b+4c}\leq \frac{1}{6}$
Cho $a, b,c >0$ và $a+b+c=2$
cmr $A=\sqrt{2a+bc}+\sqrt{2b+ac}+\sqrt{2c+ab}\leq 4$
4. cho $a, b,c>0$ và $a+b+c=1$
Tìm min $A=\frac{a}{\sqrt{1-a}}+\frac{b}{\sqrt{1-b}}+\frac{c}{\sqrt{1-c}}$