Toán Lớp 8: Help ạ
Mong mọi người help em ạ !!!!!!!!!!!!!!!!!!!!!!!!!!!!
Tìm x sau :
3x(x-2)=1-x
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Toán Lớp 8: Help ạ
Mong mọi người help em ạ !!!!!!!!!!!!!!!!!!!!!!!!!!!!
Tìm x sau :
3x(x-2)=1-x
Comments ( 2 )
3x\left( {x – 2} \right) = 1 – x\\
\Leftrightarrow 3{x^2} – 6x = 1 – x\\
\Leftrightarrow 3{x^2} – 5x – 1 = 0\\
\Leftrightarrow {x^2} – \dfrac{5}{3}x – \dfrac{1}{3} = 0\\
\Leftrightarrow {x^2} – 2.x.\dfrac{5}{6} + \dfrac{{25}}{{36}} – \dfrac{{25}}{{36}} – \dfrac{1}{3} = 0\\
\Leftrightarrow {\left( {x – \dfrac{5}{6}} \right)^2} = \dfrac{{37}}{{36}}\\
\Leftrightarrow \left[ \begin{array}{l}
x – \dfrac{5}{6} = \dfrac{{\sqrt {37} }}{6}\\
x – \dfrac{5}{6} = – \dfrac{{\sqrt {37} }}{6}
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{{5 + \sqrt {37} }}{6}\\
x = \dfrac{{5 – \sqrt {37} }}{6}
\end{array} \right.\\
Vậy\,x = \dfrac{{5 + \sqrt {37} }}{6};x = \dfrac{{5 – \sqrt {37} }}{6}
\end{array}$