ta có: x+y=1\Rightarrow x=1-y;y=1-x thay vào P$P=\frac{1-y}{y+1}+\frac{1-x}{x+1}=2(\frac{1}{x+1}+\frac{1}{y+1})-2\geq \frac{4}{x+y+2}-2=\frac{2}{3}"=" khi x=y=\frac{1}{2}$
ta có:
x+y=1\Rightarrow x=1-y;y=1-x thay vào
P$P=\frac{1-y}{y+1}+\frac{1-x}{x+1}=2(\frac{1}{x+1}+\frac{1}{y+1})-2\geq \frac{
8}{x+y+2}-2=\frac{2}{3}
"=" khi x=y=\frac{1}{2}$