Toán Lớp 9: 2a+b=1;5a+b=-1 thì a với b bằng mấy ạ
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Toán Lớp 9: 2a+b=1;5a+b=-1 thì a với b bằng mấy ạ
Comments ( 2 )
\left\{ \begin{array}{l}
2a + b = 1\left( 1 \right)\\
5a + b = – 1\left( 2 \right)
\end{array} \right.\\
\left( 2 \right) – \left( 1 \right): \Leftrightarrow 3a = – 2\\
\Leftrightarrow a = – \dfrac{2}{3}\\
\Rightarrow \left\{ \begin{array}{l}
a = – \dfrac{2}{3}\\
b = 1 – 2a
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
a = – \dfrac{2}{3}\\
b = 1 – 2\left( { – \dfrac{2}{3}} \right) = \dfrac{7}{3}
\end{array} \right.\\
\Rightarrow \left( {a;b} \right) = \left( { – \dfrac{2}{3};\dfrac{7}{3}} \right)
\end{array}$