a: Thay x=9 vào B, ta được:
\(B=\dfrac{9+27}{3-2}=36\)
b: \(A=\dfrac{2x-\sqrt{x}+4-x-3\sqrt{x}}{\sqrt{x}\left(\sqrt{x}+3\right)}\cdot\dfrac{\sqrt{x}}{\sqrt{x}-2}\)
\(=\dfrac{\left(\sqrt{x}-2\right)^2}{\sqrt{x}+3}\cdot\dfrac{1}{\sqrt{x}-2}=\dfrac{\sqrt{x}-2}{\sqrt{x}+3}\)