\(\Leftrightarrow\left(1+x\sqrt{x^2+1}\right)\left(\sqrt{x^2+1}-x\right)=\left(\sqrt{x^2+1}-x\right)\left(\sqrt{x^2+1}+x\right)\)
\(\Leftrightarrow\left(\sqrt{x^2+1}-x\right)\left(1+x\sqrt{x^2+1}-\sqrt{x^2+1}-x\right)=0\)
\(\Leftrightarrow\left(\sqrt{x^2+1}-x\right)\left(\sqrt{x^2+1}-1\right)\left(x-1\right)=0\)
Tự giải tiếp nhé