1.c) $x^2+2\geq 2\sqrt{2}x$( cauchy)$\Rightarrow \frac{1}{x^2+2}\leq \frac{1}{2\sqrt{2}x}\Leftrightarrow \frac{x}{x^2+2} \leq \frac{1}{2\sqrt{2}}=\frac{\sqrt{2}}{4}$"=" khi $x=\sqrt{2}$d) tương tự ^^
1.c) $x^2+2\geq 2\sqrt{2}x$( cauchy)$\Rightarrow \frac{1}{x^2+2}\leq \frac{1}{2\sqrt{2}x}\Leftrightarrow \frac{x}{x^2+2} \leq \frac{1}{2\sqrt{2}}=\frac{\sqrt{2}}{4}$"=" khi $x=\sqrt{2}$
1.c) $x^2+2\geq 2\sqrt{2}x$( cauchy)$\Rightarrow \frac{1}{x^2+2}\leq \frac{1}{2\sqrt{2}x}\Leftrightarrow \frac{x}{x^2+2} \leq \frac{1}{2\sqrt{2}}=\frac{\sqrt{2}}{4}$"=" khi $x=\sqrt{2}$
d) tương tự ^^