a: \(\Leftrightarrow\left\{{}\begin{matrix}6x+3y=15\\x-3y=-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}7x=14\\2x+y=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=1\end{matrix}\right.\)
b: \(P=\dfrac{1}{x_1}+\dfrac{1}{x_2}=\dfrac{x_1+x_2}{x_1x_2}=\dfrac{1}{3}:\dfrac{-2}{3}=\dfrac{-1}{2}\)
a.\(\Leftrightarrow\left\{{}\begin{matrix}2\left(3y-1\right)+y=5\\x=3y-1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}6y-2+y=5\\x=3y-1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}7y=7\\x=3y-1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=1\\x=3.1-1=2\end{matrix}\right.\)
