\(\Rightarrow\left\{{}\begin{matrix}\dfrac{5}{x+y}-\dfrac{4}{x-y}=0\\\dfrac{40}{x+y}+\dfrac{40}{x-y}=9\end{matrix}\right.\)
Đặt \(\left\{{}\begin{matrix}\dfrac{1}{x+y}=u\\\dfrac{1}{x-y}=v\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}5u-4v=0\\40u+40v=9\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}u=\dfrac{1}{10}\\v=\dfrac{1}{8}\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}\dfrac{1}{x+y}=\dfrac{1}{10}\\\dfrac{1}{x-y}=\dfrac{1}{8}\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x+y=10\\x-y=8\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x=9\\y=1\end{matrix}\right.\)
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