Lời giải:
HPT \(\Leftrightarrow \left\{\begin{matrix} 3x=9+7y\\ \frac{5}{3x+3y}-\frac{2}{3x-3y}=\frac{1}{3}\end{matrix}\right.\)
\(\Rightarrow \frac{5}{9+7y+3y}-\frac{2}{9+7y-3y}=\frac{1}{3}\)
\(\Leftrightarrow \frac{5}{9+10y}-\frac{2}{9+4y}=\frac{1}{3}\)
\(\Leftrightarrow \frac{45+20y-18-20y}{(9+10y)(9+4y)}=\frac{1}{3}\)
\(\Leftrightarrow \frac{27}{40y^2+126y+81}=\frac{1}{3}\)
\(\Rightarrow 40y^2+126y+81=81\)
\(\Leftrightarrow 40y^2+126y=0\)
\(\Leftrightarrow 2y(20y+63)=0\Rightarrow \left[\begin{matrix} y=0\\ y=-\frac{63}{20}\end{matrix}\right.\)
Nếu \(y=0\Rightarrow x=\frac{9+7y}{3}=3\)
Nếu \(y=\frac{-63}{20}\Rightarrow x=\frac{9+7y}{3}=\frac{-87}{20}\)
Vậy........
