1, cho x,y,z > 0 & $x^{2} + y^{2 } + z^{2} = 2014$
Tìm GTNN của $P= \frac{xy}{z}+\frac{yz}{x}+\frac{zx}{y}$
2,cho a, b, c > 0 & a + b +c =3.
cmr $\frac{a^{3}}{a+bc}+\frac{b^{3}}{b+ca}+\frac{c^{3}}{c+ab}\geq \frac{3}{3}$
3, a,b,c>0 & ab + bc + ca =3. cmr $\frac{1}{1+ a^{2}\left ( b+c \right )}+ \frac{1}{1+b^{2}+\left ( c+a \right )}+\frac{1}{1+c^{2}\left ( a+b \right )}\leq \frac{1}{abc}$