\(x+\sqrt{x^2+2011}=\frac{2011}{y+\sqrt{y^2+2011}}=\sqrt{y^2+2011}-y\) ( 1 )
tương tự: \(y+\sqrt{y^2+2011}=\sqrt{x^2+2011}-x\) ( 2 )
từ ( 1 ) và ( 2 ): \(\Rightarrow x+y+\sqrt{x^2+2011}+\sqrt{y^2+2011}\)
\(=\sqrt{x^2+2011}+\sqrt{y^2+2011}-\left(x+y\right)\)
\(\Rightarrow2\left(x+y\right)0\)
\(\Rightarrow x+y=0\)