CÁc sư phụ cho em hỏi bài violympic này ạ

E

eye_smile

$\dfrac{{{x^4} - 5{x^2} + 4}}{{{x^4} - 10{x^2} + 9}} = 0 \leftrightarrow \left\{ \begin{array}{l}
{x^4} - 5{x^2} + 4 = 0 \\
{x^4} - 10{x^2} + 9 \ne 0 \\
\end{array} \right. \leftrightarrow \left\{ \begin{array}{l}
\left( {x - 2} \right)\left( {x + 2} \right)\left( {x - 1} \right)\left( {x + 1} \right) = 0 \\
\left( {x - 3} \right)\left( {x + 3} \right)\left( {x - 1} \right)\left( {x + 1} \right) \ne 0 \\
\end{array} \right.$
$ \leftrightarrow \left\{ \begin{array}{l}
\left( {x - 2} \right)\left( {x + 2} \right)\left( {x - 1} \right)\left( {x + 1} \right) = 0 \\
x \ne \pm 3;x \ne \pm 1 \\
\end{array} \right. \leftrightarrow x = \pm 2$
 
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