9. [tex] \frac{x^{2}-x+1+2(x+1)}{x^{3}+1}\leq \frac{2x+3}{x^{3}+1} <=> \frac{x^{2}-x}{x^{3}+1}\leq 0[/tex]
<=> [tex]\left\{\begin{matrix} x^{2}-x\leq 0 & & \\ x^{3}+1\geq 0 & & \end{matrix}\right.[/tex]
<=> [tex]\left\{\begin{matrix} x(x-1)\leq 0 & & \\ -1 \leq x & & \end{matrix}\right.[/tex] [tex]\left\{\begin{matrix} 0\leq x\leq 1 & & \\ -1\leq x & & \end{matrix}\right.[/tex]
TH2: tự giải[tex]\left\{\begin{matrix} \left\{\begin{matrix} x\leq 0 & & \\ 1\leq x & & \end{matrix}\right.& & \\ x\leq -1 & & \end{matrix}\right.[/tex]
Tự kết luận
10. [tex]<=> \frac{(x-1)(x-2)}{(x-5)(x-3)}\geq 0
TH1 : <=> \left\{\begin{matrix} (x-1)(x-2)\geq 0 & & \\ (x-5)(x-3)\geq 0 & & \end{matrix}\right. <=> \left\{\begin{matrix} x\leq 1, 2\leq x & & \\ x\leq 3, 5\leq x & & \end{matrix}\right.[/tex]
TH2: Tương tự.