Rút gọn biểu thức sau: $A=\frac{a-\sqrt{a}}{a-1}$$-\frac{\sqrt{a}-1}{\sqrt{a}+1}$ $(a$ $\geq0; a$ $\neq1)$

`A=(a-sqrta)/(a-1)-(sqrta-1)/(sqrta+1)(a>=0;ane1)`

`=(sqrta(sqrta-1))/((sqrta-1)(sqrta+1))+(-(sqrta-1))/(sqrta+1)`

`=sqrta/(sqrta+1)+(-sqrta+1)/(sqrta+1)`

`=(sqrta-sqrta+1)/(sqrta+1)`

`=1/(sqrta+1)`