Bài 2:
1: Khi x=49 thì \(A=\dfrac{7-2}{7}=\dfrac{5}{7}\)
2: \(=\dfrac{2x-6\sqrt{x}+x+3\sqrt{x}-2x}{x-9}=\dfrac{x-3\sqrt{x}}{x-9}=\dfrac{\sqrt{x}}{\sqrt{x}+3}\)
3: \(P=A\cdot B=\dfrac{\sqrt{x}}{\sqrt{x}+3}\cdot\dfrac{\sqrt{x}-2}{\sqrt{x}}=\dfrac{\sqrt{x}-2}{\sqrt{x}+3}\)
Để P<0 thì căn x-2<0
=>0<x<4
=>\(x\in\left\{1;2;3\right\}\)