\(a)A=\dfrac{x^2-\sqrt{x}}{x+\sqrt{x}+1}-\dfrac{x^2+\sqrt{x}}{x-\sqrt{x}+1}\\ A=\dfrac{\sqrt{x}\left(x\sqrt{x}-1\right)}{x+\sqrt{x}+1}-\dfrac{\sqrt{x}\left(x\sqrt{x}+1\right)}{x-\sqrt{x}+1}\\ A=\dfrac{\sqrt{x}\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}{x+\sqrt{x}+1}-\dfrac{\sqrt{x}\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)}{x-\sqrt{x}+1}\\ A=\sqrt{x}\left(\sqrt{x}-1\right)-\sqrt{x}\left(\sqrt{x}+1\right)\\ A=x-\sqrt{x}-x-\sqrt{x}=-2\sqrt{x}\)
\(B=A+x-1\)
\(=x-2\sqrt{x}-1\)
\(=\left(x-2\sqrt{x}+1\right)-2\)
\(=\left(\sqrt{x}-1\right)^2-2\ge-2\)
Vậy GTNN của B là -2 khi \(x=1\)