giúp đi mn :<< cần gấp

$ P = ( \dfrac{1-a\sqrt[]{a}}{1-\sqrt[]{a}} + \sqrt[]{a} ) ( \dfrac{1-\sqrt[]{a}}{1-a} )^2 $

$ = [ \dfrac{(1-\sqrt[]{a})(1+\sqrt[]{a}+1)}{1-\sqrt[]{a}} + \sqrt[]{a} ] [ \dfrac{1-\sqrt[]{a}}{(1-\sqrt[]{a})(1+\sqrt[]{a})} ]^2 $

$ = ( 1 + \sqrt[]{a} + a + \sqrt[]{a} ) ( \dfrac{1}{1+\sqrt[]{a}})^2$

$ = ( 1 + \sqrt[]{a} )^2 . \dfrac{1}{(1+\sqrt[]{a})^2} $

$ = 1 $