Toán Lớp 7: Tìm x thuộc Z biết: x/3 < 3/2 < x+1/3 Tìm x
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Toán Lớp 7: Tìm x thuộc Z biết: x/3 < 3/2 < x+1/3 Tìm x
Comments ( 2 )
\dfrac{x}{3} < \dfrac{3}{2} < \dfrac{{x + 1}}{3}\\
\Leftrightarrow \dfrac{{2.x}}{6} < \dfrac{{3.3}}{6} < \dfrac{{2\left( {x + 1} \right)}}{6}\\
\Leftrightarrow 2x < 9 < 2x + 2\\
\Leftrightarrow \left\{ \begin{array}{l}
x < \dfrac{9}{2}\\
2x > 7
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x < 4,5\\
x > 3,5
\end{array} \right.\\
\Leftrightarrow 3,5 < x < 4,5\\
Do:x \in Z\\
\Leftrightarrow x = 4\\
Vậy\,x = 4
\end{array}$
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