\(\left\{{}\begin{matrix}2x-y=5\\x+3y=1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}2x-y=5\\-2x-6y=-2\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}-7y=3\\x+3y=1\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=1+\dfrac{\left(-3\right).\left(-3\right)}{7}\\y=-\dfrac{3}{7}\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{16}{7}\\y=-\dfrac{3}{7}\end{matrix}\right.\)

\(x^4+2x^3-6x-9\)

\(=x^4+ 2x^3+3x^2-3x^2-6x-9\)

\(=x^2\left(x^2+2x+3\right)-3\left(x^2+2x+3\right)\)

\(=\left(x^2-3\right)\left(x^2+2x+3\right)\)

\(\frac{51}{61}\)

Thanks

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tk mình nha

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