Bài 2
a) A\(=\sqrt{\left(\sqrt{7}+1\right)^2}-\sqrt{\left(2+\sqrt{7}\right)^2}=\sqrt{7}+1-2-\sqrt{7}=-1\)
b)B=\(\left(\dfrac{x-4-x+2\sqrt{x}}{x-4}\right).\dfrac{\sqrt{x}+2}{x}=\dfrac{2\left(\sqrt{x}-2\right)}{\left(\sqrt{x}-2\right)\sqrt{x}}=\dfrac{2}{\sqrt{x}}\)