đk : \(\left(x\ne1;y\ne1;x;y\ge0\right)\)
\(\dfrac{x-1}{\sqrt{y}-1}\sqrt{\dfrac{\left(y-2\sqrt{y}+1\right)^2}{\left(x-1\right)^4}}\) = \(\dfrac{x-1}{\sqrt{y}-1}\sqrt{\dfrac{\left(\left(\sqrt{y}-1\right)^2\right)^2}{\left(\left(x-1\right)^2\right)^2}}\)
= \(\dfrac{x-1}{\sqrt{y}-1}\dfrac{\left(\sqrt{y}-1\right)^2}{\left(x-1\right)^2}\) = \(\dfrac{\sqrt{y}-1}{x-1}\)