C1: \(\frac{x^2}{y^2}+\frac{y^2}{x^2}+4\ge3\left(\frac{x}{y}+\frac{y}{x}\right)\)
Đặt \(t=\frac{x}{y}+\frac{y}{x}\ge2\Rightarrow t^2=\frac{x^2}{y^2}+\frac{y^2}{x^2}+2\):
\(t^2+2\ge3t\Leftrightarrow\left(t-2\right)\left(t-1\right)\ge0\forall t\ge2\) *đúng*
C2: \(BDT\Leftrightarrow\frac{\left(x-y\right)^2\left(x^2-xy+y^2\right)}{x^2y^2}\ge0\)*đúng*