Pt: $\Leftrightarrow (x^2-3x+1)\left ( \frac{x^2+x+8}{x^2-x+3+\sqrt{x^2+17x+1}}+\frac{1}{x+\sqrt{3x-1}} \right )=0$ Bất :v $a=\frac{3}{x},b=\frac{4}{y},c=\frac{5}{z}(a,b,c> 0) =>ab+bc+ac\leq 1 $ $=> P=\frac{a}{\sqrt{1+a^{2}}}+\frac{b}{\sqrt{1+b^{2}}}+\frac{c}{\sqrt{1+c^{2}}}$ $\leq \frac{a}{\sqrt{ab+bc+ac+a^{2}}}+\frac{b}{\sqrt{b^{2}+ab+bc+ac}}+\frac{c}{\sqrt{ab+bc+ac+c^{2}}}$ $=\frac{a}{\sqrt{(a+b)(a+c)}}+\frac{b}{\sqrt{(b+c)(a+b)}}+\frac{c}{\sqrt{(a+c)(b+c)}}$ $\leq \frac{1}{2}(\frac{a}{a+b}+\frac{a}{a+c}+\frac{b}{b+c}+\frac{b}{a+b}+\frac{c}{a+c}+\frac{c}{b+c})\doteq \frac{3}{2}$ #tham khảo -=-
