a; Thay x=1/4 vào A, ta được:
\(A=\left(\dfrac{1}{2}+3\right):\left(\dfrac{1}{2}-2\right)=\dfrac{7}{2}:\dfrac{-3}{2}=\dfrac{-7}{3}\)
b: \(B=\dfrac{x-2\sqrt{x}+2\sqrt{x}+2-3}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-2\right)}=\dfrac{\sqrt{x}-1}{\sqrt{x}-2}\)