Khá hack não bài nào phải xét dấu = @@
[tex]P = \frac{1}{4x^{2} + 2} + \frac{1}{4y^{2} + 2} + \frac{2}{xy}\geq \frac{4}{4(x^2+y^2)+4}+\frac{2}{xy}=\frac{4}{4(x^2+y^2)+4}+\frac{4}{12xy}+\frac{5}{3xy}\geq \frac{16}{4(x+y)^2+4+4xy}+\frac{5}{3xy}\\2=x+y\geq 2\sqrt{xy}\rightarrow xy\leq 1\\\frac{16}{4(x+y)^2+4+4xy}+\frac{5}{3xy}\geq \frac{16}{4.2^2+4+4.1}+\frac{5}{3.1}=\frac{7}{3}\\"="x=y=1[/tex]