a: \(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{3}{x}-\dfrac{3}{y}=15\\\dfrac{3}{x}-\dfrac{2}{y}=12\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-\dfrac{1}{y}=3\\\dfrac{1}{x}-\dfrac{1}{y}=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{1}{3}\\x=\dfrac{1}{2}\end{matrix}\right.\)
b: \(\Leftrightarrow\left\{{}\begin{matrix}6\left|x+1\right|-4\left|y+2\right|=-2\\6\left|x+1\right|+9\left|y+2\right|=24\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left|y+2\right|=2\\\left|x+1\right|=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\in\left\{0;-2\right\}\\y\in\left\{0;-4\right\}\end{matrix}\right.\)
