có P = 1+x + x21−x+1+y + y21−y + 1x+y -2 = 11−x + 11−y + 1x+y -2 có ((1-x)+(1-y)+(x+y)) ( 11−x + 11−y + 1x+y ≥ 9 ⇒ 11−x + 11−y + 1x+y ≥ 92 ⇒ P ≥ 52 dấu "=" ⇔ x=y= 13
có P = 1+x +
x21−x+1+y +
y21−y +
1x+y -2 =
11−x +
11−y +
1x+y -2 có ((1-x)+(1-y)+(x+y)) (
11−x +
11−y + $\frac{1}{x+y}
)\geq
9\Rightarrow
\frac{1}{1-x}
+\frac{1}{1-y}
+\frac{1}{x+y}
\geq
\frac{9}{2}
\Rightarrow
P\geq
\frac{5}{2}
dấu"="\Leftrightarrow
x=y=\frac{1}{3}$