Giải các BĐT sau:
$1$ Cho $a,b,c>0$. CMR: $\frac{(a+b+c)^3}{abc}+\frac{ab+bc+ca}{a^2+b^2+c^2}\geq 28$
$2$ Cho $a,b,c>0$. CMR: $\sum \frac{1}{a\sqrt{3a+2b}}\geq \frac{3}{\sqrt{5abc}}$
$3$ Cho $a,b,c>0$. CMR: $\sum \frac{a^3}{(a+b)^3}\geq \frac{3}{8}$
$4$ Cho $a,b,c>0: a+b+c=3$. CMR: $\sum a\sqrt{b^3+1}\leq 5$
$5$ Cho $a,b,c>0: abc=1$. CMR: $\sum \frac{a}{b}\geq \sum a$