2a+b=1;5a+b=-1 thì a với b bằng mấy ạ

$\begin{array}{l}
\left\{ \begin{array}{l}
2a + b = 1\left( 1 \right)\\
5a + b =  - 1\left( 2 \right)
\end{array} \right.\\
\left( 2 \right) - \left( 1 \right): \Leftrightarrow 3a =  - 2\\
 \Leftrightarrow a =  - \dfrac{2}{3}\\
 \Rightarrow \left\{ \begin{array}{l}
a =  - \dfrac{2}{3}\\
b = 1 - 2a
\end{array} \right.\\
 \Rightarrow \left\{ \begin{array}{l}
a =  - \dfrac{2}{3}\\
b = 1 - 2\left( { - \dfrac{2}{3}} \right) = \dfrac{7}{3}
\end{array} \right.\\
 \Rightarrow \left( {a;b} \right) = \left( { - \dfrac{2}{3};\dfrac{7}{3}} \right)
\end{array}$