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} $\geq 2+\frac{3}{2}+2=\frac{9}{2}dấu"=" \Leftrightarrow x=y=2$
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} $\geq
1+\frac{3}{2}+2=\frac{9}{2}
dấu"=" \Leftrightarrow x=y=2$