Toán Lớp 9: giúp mk 1 câu thui
2x + 3$\sqrt{2x – 5}$ = 9
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Toán Lớp 9: giúp mk 1 câu thui
2x + 3$\sqrt{2x – 5}$ = 9
Comments ( 1 )
DK:x \ge \dfrac{5}{2}\\
2x + 3\sqrt {2x – 5} = 9\\
\to 3\sqrt {2x – 5} = 9 – 2x\\
\to 9\left( {2x – 5} \right) = 81 – 36x + 4{x^2}\left( {DK:\dfrac{9}{2} \ge x} \right)\\
\to 4{x^2} – 54x + 126 = 0\\
\to \left( {2x – 21} \right)\left( {x – 3} \right) = 0\\
\to \left[ \begin{array}{l}
x = \dfrac{{21}}{2}\left( l \right)\\
x = 3
\end{array} \right.\\
\to x = 3
\end{array}\)