Cho hai biểu thức

cho hai bieu thuc A=$\raisebox{1ex}{$\sqrt{x+4}$}\!\left/ \!\raisebox{-1ex}{$\sqrt{x-1}$}\right.$ va B= $3\raisebox{1ex}{$\sqrt{x+1}$}\!\left/ \!\raisebox{-1ex}{$x+2\sqrt{x}-3-2/\sqrt{x+3}$}\right.$, voi x$\ge$0,x khac 0
1) tinh gi tri bieu thuc A khi x=9
2)Chung minh B=$\frac{1}{\sqrt{x-1}}$
3)tim tat ca gia tri x de $\frac{A}{B}$$\ge \frac{x}{4}+5$