nguyenanhshaff

Làm sao để ấn trên máy tính casio ạ

$\frac{1}{x}+\frac{4}{y}\leq 3\Rightarrow \frac{4x+y}{xy}\leq 3\Rightarrow 4x+y\leq 3xy\Rightarrow x+y+3x\leq 3xy\Rightarrow 3+3x\leq 3xy\Rightarrow 3xy-3x\geq 3\Rightarrow 3x(y-1)\geq 3\Rightarrow x(y-1)\geqslant 1$

$\frac{x}{y+1}+\frac{y}{x+1}=\frac{x+y+1}{y+1}+\frac{x+y+1}{x+1}-2=\frac{2}{y+1}+\frac{2}{x+1}=2(\frac{1}{y+1}+\frac{1}{x+1})-2$$\geq 2(\frac{1}{2}+\frac{1}{2})-2=0$