Đặt \(\left\{{}\begin{matrix}\frac{1}{x-y}=a\\\frac{1}{x+y}=b\end{matrix}\right.\)
hpt \(\Leftrightarrow\left\{{}\begin{matrix}2a+6b=1,1\\4a-9b=1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}a=\frac{9b+1}{4}\\\frac{2\cdot\left(9b+1\right)}{4}-9b=1\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}b=\frac{-1}{9}\\a=\frac{9b+1}{4}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}a=0\\b=\frac{-1}{9}\end{matrix}\right.\)
Pt vô nghiệm.