\(\sqrt{2x+2\sqrt{x^2-1}}=\sqrt{x+1+2\sqrt{\left(x+1\right)\left(x-1\right)}+x-1}\)
\(=\sqrt{\left(\sqrt{x+1}+\sqrt{x-1}\right)^2}=\sqrt{x+1}+\sqrt{x-1}\)
b/ \(\sqrt{x-1}+\sqrt{x+1}=\sqrt{7}\) (ĐKXĐ: ...)
\(\Leftrightarrow2x+2\sqrt{x^2-1}=7\)
\(\Leftrightarrow2\sqrt{x^2-1}=7-2x\) (\(x\le\frac{7}{2}\))
\(\Leftrightarrow4\left(x^2-1\right)=\left(7-2x\right)^2\)
\(\Leftrightarrow28x=53\)
\(\Leftrightarrow x=\frac{53}{28}\)