1,
thay x = 9 vào A ta có :
$\frac{√9+4}{√9-1}$
=$\frac{7}{8}$
Vậy A=$\frac{7}{8}$ khi x=9
2, B= $\frac{3√x +1}{x-2√x -3}$ - $\frac{2}{√x +3}$
=$\frac{3√x +1}{(√x -1)(√x +3)}$ -$\frac{2(√x -1)}{(√x -1)(√x +3)}$
=$\frac{3√x +1-2√x+2}{(√x -1)(√x +3)}$
=$\frac{√x+3}{(√x -1)(x +3)}$
=$\frac{1}{(√x -1)}$
