donbau

cho xyz=1 chung minh

$P= \frac{x^{2}}{x+y+y^{3}z}+\frac{y^{2}}{y+z+z^{3}x}++\frac{z^{2}}{z+x+x^{3}y}\leq 1$

$(x+\sqrt{1+y^{2}})(y+\sqrt{1+x^{2}})=1$

chứng minh $(x+\sqrt{1+x^{2}})(y+\sqrt{1+y^{2}})=1$