giải các hệ pt a) $\left \{ {{2x-y=7} \atop {3x.7 .2y=14}} \right.$

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1. $2x-y=7\Leftrightarrow y=2x-7$

   $3x.7.2y=14$

   $\Leftrightarrow xy=\dfrac{1}{3}$

   $\Leftrightarrow 3xy=1$

   $\Leftrightarrow 3x(2x-7)=1$

   $\Leftrightarrow 6x^2-21x-1=0$

   $\Leftrightarrow x=\dfrac{21\pm\sqrt{463}}{12}$

   $\to (x;y)=\Big( \dfrac{21+\sqrt{463}}{12}; \dfrac{-21+\sqrt{463}}{6}\Big), \Big(\dfrac{-21-\sqrt{463}}{12};\dfrac{-21-\sqrt{463}}{6}\Big)$

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