a)\(\left\{{}\begin{matrix}8x-7y=5\\12x+13y=-8\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}24x-21y=15\\24x+26y=-16\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}-47y=31\\24x+26y=-16\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{31}{47}\\24x+26\cdot\left(-\dfrac{31}{47}\right)=-16\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{31}{47}\\24x=\dfrac{54}{47}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-\dfrac{31}{47}\\x=\dfrac{9}{188}\end{matrix}\right.\)
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