Toán Lớp 7: tìm x,y cho 2 x+y =-14 biết x/y-7 =3/4
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Toán Lớp 7: tìm x,y cho 2 x+y =-14 biết x/y-7 =3/4
Comments ( 1 )
2x + y = – 14\\
\dfrac{x}{{y – 7}} = \dfrac{3}{4}\\
\Leftrightarrow \dfrac{x}{3} = \dfrac{{y – 7}}{4} = \dfrac{{2x}}{6}\\
= \dfrac{{2x + y – 7}}{{6 + 4}} = \dfrac{{ – 14 – 7}}{{10}} = \dfrac{{ – 21}}{{10}}\\
\Leftrightarrow \left\{ \begin{array}{l}
x = – \dfrac{{21}}{{10}}.3 = – \dfrac{{63}}{{10}}\\
y – 7 = – \dfrac{{21}}{{10}}.4 = – \dfrac{{42}}{5}
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x = \dfrac{{ – 63}}{{10}}\\
y = – \dfrac{{42}}{5} + 7 = \dfrac{{ – 7}}{5}
\end{array} \right.\\
Vậy\,x = – \dfrac{{63}}{{10}};y = – \dfrac{7}{5}
\end{array}$