a: \(=\dfrac{x\sqrt{x}+26\sqrt{x}-19-2x-6\sqrt{x}+x-4\sqrt{x}+3}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-1\right)}\)
\(=\dfrac{x\sqrt{x}-x+16\sqrt{x}-16}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-1\right)}=\dfrac{x+16}{\sqrt{x}+3}\)
b: Khi x=7-4 căn 3 thì \(C=\dfrac{7-4\sqrt{3}+16}{2-\sqrt{3}+3}=\dfrac{23-4\sqrt{3}}{5-\sqrt{3}}\)