Có:\(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{xy}{5y}=\dfrac{140}{5y}\)
\(\Rightarrow\dfrac{y}{7}=\dfrac{140}{5y}\Rightarrow5y^2=980\Rightarrow y^2=196\)
\(\Rightarrow\left[{}\begin{matrix}y=14\\y=-14\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{140}{14}=10\\x=\dfrac{140}{-14}=-10\end{matrix}\right.\)
Vậy có 2 cặp gt (x;y) t/m là: (10;14) ; (-10;-14)
