a) \(P=\frac{x^2-9}{x-3}+\frac{4-4\sqrt{x}+x}{2-\sqrt{x}}+\frac{4-x}{2+\sqrt{x}}\)
\(=\frac{\left(x-3\right)\left(x+3\right)}{x-3}+\frac{\left(2-\sqrt{x}\right)^2}{2-\sqrt{x}}+\frac{\left(2-\sqrt{x}\right)\left(2+\sqrt{x}\right)}{2+\sqrt{x}}\)
\(x+3+2-\sqrt{x}+2-\sqrt{x}\) = \(x+7-2\sqrt{x}\)
b) Tại x = 9, ta có:
P = \(x+7-2\sqrt{x}\) = 9 + 7 - 2\(\sqrt{9}\) = 10