$A=\frac{3x}{4}+\frac{1}{x}+\frac{2}{y^{2}}+y$ $=\frac{x}{4}+\frac{1}{x}+2(\frac{1}{y^{2}}+\frac{y}{8}+\frac{y}{8})+ \frac{x+y}{2}$ $\geq 1+\frac{3}{2}+2(cosi)$ $=\frac{9}{2}$dấu"=" $\Leftrightarrow x=y=2$
$A=\frac{3x}{4}+\frac{1}{x}+\frac{2}{y^{2}}+y$ $=\frac{x}{4}+\frac{1}{x}+2(\frac{1}{y^{2}}+\frac{y}{8}+\frac{y}{8})+ \frac{x+y}{2}$ $\geq 1+\frac{3}{2}+2=\frac{9}{2}$dấu"=" $\Leftrightarrow x=y=2$
$A=\frac{3x}{4}+\frac{1}{x}+\frac{2}{y^{2}}+y$ $=\frac{x}{4}+\frac{1}{x}+2(\frac{1}{y^{2}}+\frac{y}{8}+\frac{y}{8})+ \frac{x+y}{2}$ $\geq 1+\frac{3}{2}+2
(cosi)$ $=\frac{9}{2}$dấu"=" $\Leftrightarrow x=y=2$