a: Sửa đề: \(\sqrt{20}+3\sqrt{18}+\sqrt{80}+\sqrt{50}\)
\(=2\sqrt{5}+9\sqrt{2}+4\sqrt{5}+5\sqrt{2}\)
\(=14\sqrt{2}+6\sqrt{5}\)
b: \(A=\dfrac{x-\sqrt{x}-2-\left(x+\sqrt{x}-2\right)}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)
\(=\dfrac{x-\sqrt{x}-2-x-\sqrt{x}+2}{x-1}=\dfrac{-2\sqrt{x}}{x-1}\)