Toán Lớp 7: a) 2 . ( x – 1/2 ) – 5 ( x + 3/5 ) = -x + 1/3
b) x/4 = y/3 = z/5 và x + 2y – z = -20
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Toán Lớp 7: a) 2 . ( x – 1/2 ) – 5 ( x + 3/5 ) = -x + 1/3
b) x/4 = y/3 = z/5 và x + 2y – z = -20
Comments ( 2 )
a)2.\left( {x – \dfrac{1}{2}} \right) – 5.\left( {x + \dfrac{3}{5}} \right) = – x + \dfrac{1}{3}\\
\Leftrightarrow 2x – 1 – 5x – 3 = – x + \dfrac{1}{3}\\
\Leftrightarrow 2x – 5x + x = \dfrac{1}{3} + 1 + 3\\
\Leftrightarrow – 2x = \dfrac{{13}}{3}\\
\Leftrightarrow x = – \dfrac{{13}}{6}\\
Vậy\,x = – \dfrac{{13}}{6}\\
b)\dfrac{x}{4} = \dfrac{y}{3} = \dfrac{z}{5} = \dfrac{{2y}}{6}\\
= \dfrac{{x + 2y – z}}{{4 + 6 – 5}} = \dfrac{{ – 20}}{5} = – 4\\
\Leftrightarrow \left\{ \begin{array}{l}
x = – 4.4 = – 16\\
y = – 4.3 = – 12\\
z = – 4.5 = – 20
\end{array} \right.\\
Vậy\,x = – 16;y = – 12;z = – 20
\end{array}$