Ta có: \(A=\left(\frac{1-a\sqrt{a}}{1-\sqrt{a}}+\sqrt{a}\right)\left(\frac{1-\sqrt{a}}{1-a}\right)^2\)
\(=\left(\frac{\left(1-\sqrt{a}\right)\left(1+\sqrt{a}+a\right)}{1-\sqrt{a}}+\sqrt{a}\right)\cdot\left(\frac{1-\sqrt{a}}{\left(1-\sqrt{a}\right)\left(1+\sqrt{a}\right)}\right)^2\)
\(=\left(a+\sqrt{a}+\sqrt{a}+1\right)\cdot\left(\frac{1}{\sqrt{a}+1}\right)^2\)
\(=\left(a+2\sqrt{a}+1\right)\cdot\frac{1}{\left(\sqrt{a}+1\right)^2}\)
\(=\frac{\left(\sqrt{a}+1\right)^2}{\left(\sqrt{a}+1\right)^2}=1\)