Câu trả lời:
\(4x=3y\Leftrightarrow x=\frac{3y}{4}\)(*)
Thay (*) vào \(\left(x-y\right)^2+\left(x+y\right)^2=50\Leftrightarrow\left(\frac{3y}{4}-y\right)^2+\left(\frac{3y}{4}+y\right)=50\Leftrightarrow\left(\frac{3y-4y}{4}\right)^2+\left(\frac{3y+4y}{4}\right)^2=50\)
\(\Leftrightarrow\frac{y^2}{16}+\frac{49y^2}{16}=50\Leftrightarrow49y^2+y^2=800\Leftrightarrow50y^2=800\Leftrightarrow y^2=16\Leftrightarrow y=4\)