

cho a,b,c >0 .cmr
[tex]\frac{xy}{x^{2}+yz+xz}+\frac{yz}{y^{2}+xz+xy}+\frac{xz}{z^{2}+xy+yz}\leq \frac{x^{2}+y^{2}+z^{2}}{xy+yz+xz}[/tex]
[tex]\frac{xy}{x^{2}+yz+xz}+\frac{yz}{y^{2}+xz+xy}+\frac{xz}{z^{2}+xy+yz}\leq \frac{x^{2}+y^{2}+z^{2}}{xy+yz+xz}[/tex]