[tex]2\geq a+\frac{4}{b}\geq 2\sqrt{\frac{4a}{b}}\Rightarrow \frac{a}{b}\leq \frac{1}{4}[/tex]
[tex]P=\frac{1}{\frac{a}{b}+\frac{2b}{a}}=\frac{1}{\frac{a}{b}+\frac{b}{16a}+\frac{31}{16}.\frac{b}{a}}\leq \frac{1}{2\sqrt{\frac{ab}{16ab}}+\frac{31}{16}.4}=...[/tex]