1/Cho a,b,c là các số thực dương. CMR $\sum_{}^{} \sqrt{a^2+(1-b)^2}\ge \frac{3\sqrt{2}}{2}$
2/Cho a,b,c $\in R^+,abc=1$. CMR: $\sum_{}^{} \frac{a+b}{\sqrt{c}}\ge \sum_{}^{}\sqrt{a}+3 $
3/Cho a,b,c $\in R^+$. CMR: $\sum_{}^{}\frac{a}{(b+c)^2}\ge\frac{9}{4(a+b+c)} $
4/Cho $a,b,c \ge 0$. CMR $\sum_{}^{}\sqrt{a^4+a^2b^2+b^4}\ge\sum_{}^{}a\sqrt{2a^2+bc} $