Hình như đề sai ! Sửa :
\(\left(\frac{1}{\sqrt{x+1}}-\sqrt{1-x}\right):\left(\frac{1}{\sqrt{1-x^2}}-1\right)\)
\(=\frac{1-\sqrt{1-x^2}}{\sqrt{1+x}}:\frac{1-\sqrt{1-x^2}}{\sqrt{1-x^2}}\)
\(=\frac{\left(1-\sqrt{1-x^2}\right)\left(\sqrt{1-x^2}\right)}{\left(\sqrt{1+x}\right)\left(1-\sqrt{1-x^2}\right)}\)
\(=\sqrt{1-x}\)