$a)A=\sqrt{x}-\sqrt{x-\sqrt{x}+\dfrac{1}{4}}\\=\sqrt{x}-\sqrt{(\sqrt{x})^2-2.\sqrt{x}.\dfrac{1}{2}+(\dfrac{1}{2})^2}\\=\sqrt{x}-\sqrt{(\sqrt{x}-\dfrac{1}{2})^2}\\=\sqrt{x}-|\sqrt{x}-\dfrac{1}{2}|\\=\left[\begin{matrix}\dfrac{1}{2}\ khi\ x\ge\dfrac{1}{4}\\2\sqrt{x}-\dfrac{1}{2}\ khi\ 0\le x<\dfrac{1}{4}\end{matrix}\right.$
$b)B=\sqrt{4x-2\sqrt{4x-1}}+\sqrt{4x+2\sqrt{4x-1}}\\=\sqrt{4x-1-2\sqrt{4x-1}+1}+\sqrt{4x-1+2\sqrt{4x-1}+1}\\=\sqrt{(\sqrt{4x-1}-1)^2}+\sqrt{(\sqrt{4x-1}+1)^2}\\=|\sqrt{4x-1}-1|+|\sqrt{4x-1}+1|\\=\left[\begin{matrix}2\sqrt{4x-1}\ khi\ x\ge\dfrac{1}{2}\\2\ khi\ x<\dfrac{1}{2}\end{matrix}\right.$
